Rebuilding a Hybrid Vehicle Battery Pack


Inside this Article

2003 Honda Civic Hybrid
2003 Honda Civic Hybrid
ACCESSING THE BATTERIES - Removing the rear seat. There are three 10 mm bolts, one on either side of the seat (as shown) and one near the middle of the seat.
ACCESSING THE BATTERIES - Removing the seat reveals the main battery box cover.
LOCATING THE MAIN CIRCUIT BREAKER - Remove the main circuit breaker cover. Make sure it’s in the “off” position and remove the red plastic safety cover, breaking off the plastic pin.
LOCATING THE MAIN CIRCUIT BREAKER - Remove the main circuit breaker cover. Make sure it’s in the “off” position and remove the red plastic safety cover, breaking off the plastic pin.
GETTING TO THE BATTERIES - In the car, with the battery box cover and seats out. Note the yellow wire for the external charging port.
ACCESSING THE SENSOR WIRES - The main power connection: The three sensor connectors sit above the positive and negative wires.
FINDING THE FOURTH SENSOR - The fourth sensor connector sits below the main positive and negative wires.
THE BATTERY PACK, REMOVED - The circuit breaker fuse and the wiring side of the pack.
THE REMOVED CIRCUIT BREAKER ASSEMBLY - Take care to keep track of the twenty 10 mm bolts and temperature sensor wire routing; note the four round metal spacers—where the circuit breaker makes its electrical connections to the sticks.
REMOVING STICKS FROM THEIR HOUSING - The orange bus bar and some of the sticks are removed.
REMOVING STICKS FROM THEIR HOUSING - Each stick is fully charged before starting the discharge/charge reconditioning cycles.
CHARGING A STICK - A stick connected to the charger to be reconditioned.
FINISHED STICKS - A pile of finished sticks with final Ah ratings written on each. Note the small metal thermal sensor tabs on each stick.
2003 Honda Civic Hybrid

Reconditioning NiMh hybrid car battery packs is time-consuming—you cannot rush it! However, if you have the patience, reconditioning them yourself can save you more than 90% of the cost of having a car a dealer do the job.

Last fall, I bought my friend’s dysfunctional 2003 Civic Hybrid. It was not something I needed, but it did have only 110,000 miles on the odometer and some nice custom features—and it was cheap! Plus, it had been well-maintained: All the dealer checkups and service had been properly performed.

But besides the car’s computer spewing some error codes, it also had performance issues suggesting expensive battery problems. The car was very sluggish and its mpg had dropped off—from more than 50 mpg to 35 to 40 mpg. It stalled easily; the auto-stop function—which turns off the IC engine when the car comes to a full stop—did not work; and, of course, the “check engine” and integrated motor assist (IMA) warning lights wouldn’t shut off.

The Honda dealership wanted $3,200 to replace the battery pack with a factory-refurbished one (new cells are not available for a Civic Hybrid of that vintage). Replacement battery packs are made from dead packs dealers return to Honda, which recovers the remaining good subpacks for reuse. These refurbished packs include a one-year factory warranty. There is at least one third-party that claims to do the same thing for $1,250, but you have to sell him your old battery pack first, which he uses for salvageable parts. The few online bloggings from DIYers who tried reconditioning their own packs were not very insightful. However, by doing a lot of “reading between the lines,” I felt I learned enough to try my hand at refurbishing.

The root of the batteries’ underperformance had to do with the nickel metal hydride (NiMH) cells getting warm from discharging and charging. After thousands of cycles, the fine nickel powder inside starts to form larger nickel crystals, which eventually impede the electrons from flowing. If the crystals get big enough, they can puncture the separators between the positive and negative sides of the cell, shorting the cell. Reconditioning helps break up these crystals. Although it won’t make the cell like new, it’ll result in a better-functioning cell.

Preliminary Precautions

All you need to recondition IMA battery packs are a few basic tools: a good digital multimeter; the right charger/reconditioning machine (there are several to choose from online); a #30 Torx driver; standard hand tools; and, most importantly, the will and time to do the work right. Because this project can take several weeks of charging, you may need a second car to drive until the project is completed.

Hybrid car blogs published plenty of warnings about getting electrocuted from the batteries. Since this was new territory for me, I took this advice seriously—but there is only one place on a battery pack where any real hazard exists: from voltage across the full pack, which can be up to 180 VDC.

That single location is easily found with a multimeter, and once you turn off the IMA pack’s built-in circuit breaker and start unbolting the individual subpacks, the risk drops significantly since the sticks are only about 8 V each. Honda designed the battery pack in an almost idiot-proof way. The terminal bolts and other fasteners are arranged so that it is easy to avoid touching two ends of any higher-voltage terminals at the same time. Common sense coupled with basic mechanical skills meet most everything else you come across during this task. But working carelessly can still hurt, as well as cause you expensive additional repairs.

Dissassembling the System

Start by parking the car in a place it can stay for a month or two. Finding that you need to move the car after you’ve removed the battery pack is a real bummer, since the car will not move under its own power without a working battery pack.

Next, remove the rear seat cushions (three 10 mm bolts and some plastic clips). Then take off the small cover over the battery box’s circuit breaker (two bolts, #30 Torx), remove its red plastic safety cover and turn off the circuit breaker. The 180 VDC electrical hazard is now gone—the breaker separates about 40% of the sticks from the rest of the pack. Nonetheless, be careful as you work. To get the main cover off, you will need to break off the little black plastic safety snap/pin to the right of the circuit breaker with a large, flat screwdriver.

Remove the metal main battery box cover (six bolts, #30 Torx) and slide the entire cover up an inch or two to release the two metal fingers on the extreme right and left of the cover. You may need to have someone hold the seatbelts to one side to do this.

Once the cover is off, you will find a bewildering array of wiring and connectors. If you disconnect the 12 V battery (yes, there is a standard car battery, too) in the engine compartment, even that small hazard is eliminated. To do this, disconnect the cable at the negative battery post and insulate the end completely with electrical tape or a similar insulating material. This is safer than disconnecting the positive side and less likely to create a short to the chassis. In any case, continue to be careful not to bang up anything since replacing broken terminals or repairing cut wiring is a major and unnecessary chore.

Inside the battery box, remove the three 10 mm bolts that hold the two main IMA power wires and ground wire for the battery pack. Unplug the five sensor connectors from the pack. Then remove the four 12 mm bolts that hold the battery pack in the metal box (two on the top of the pack and two on the bottom). Gently bend any wires out of the way and lift out the battery pack. It weighs about 50 pounds and you will be stooped over in an awkward position, so protect your back and consider having a friend help with the lift.

Use the existing carry straps to lift it, being careful not to get tangled up with any wires. Take a few photos as you go along so you remember where everything goes in a month (or two) after completion.

Preparing for Reconditioning

I set up my work area in the living room, since it is climate-controlled and well-illuminated. Find an organizable work area, because there will be no less than 90 assorted bolts and screws holding the pack together. As you take apart the pack to access the subpack sticks inside, you’ll need to keep a close count of all the fasteners—use a spill-proof container! 

You cannot disassemble the sticks—they are welded together in groups of six cells and tightly wrapped in yellow plastic. These yellow sticks are what you will be “reconditioning” with your new charger/reconditioner machine. Remove each stick from the plastic holding frame to allow for easy judging of how warm each cell gets as reconditioning proceeds. Each stick has a “square” end and a “hex” end. The positive side is the square—mark it as such to avoid confusion. If you do connect the charger in the wrong polarity, it is smart enough to scream at you and display “connection reversed” before any damage can be done to the cells.

Be careful of the small sensor wires attached to three of the sticks—they pull apart easily and are a major pain to put back again. These three sticks can only be removed from the frame by firmly pushing them from right to left (looking at the pack as it would be in the car). The sensor wires are not very long, so carefully bend them so the sticks they are attached to are not pulling on them. Remember (and take photos of) how the wires are routed around the pack and where their little holders snap together. They will only fit in one way without making trouble for you when reassembly starts.

Reconditioning the Sticks

Although NiMh cells were once thought to be “memory-proof,” all nickel-based batteries develop memory problems; NiMhs are just much more resistant to the problem than NiCd cells.

Deep cycling has always been the method of minimizing, and somewhat repairing, memory issues. This is what your charger/reconditioner does, in a very sophisticated way. Its computer brain monitors the cycling cells to optimize breaking up the microscopic nickel “crystals” that form as a cell ages with use. The reconditioning is not perfect and will never make the cell factory-fresh again, but it does go far in making the cell work as well as it can.

Follow the charger manufacturer’s instructions for setting up your reconditioner for NiMh cells. Be sure you understand the instructions. I used an iMax B6 ($55) and the instructions had to have been written by someone whose English was not great—it was difficult to understand at first. 

Do not despair if the instructions are too difficult to decipher. The default settings for each type of battery (which are already programmed into the charger) seem to work well enough. But I changed the minimum cell state on mine to 0.8 V per cell, just to get a little deeper discharge and, hopefully, a more functional battery in the end. Do not discharge them too far, which can cause cell polarity reversal, which means you end up with a dead stick!

Number the sticks with a permanent black marker to avoid mixing them up. Have a pad of paper and pen handy to record the values the screen displays at the end of each programmed cycle to track how each stick performed. Believe me, after a month or more of this, it is a hopeless task remembering it all.

Fully charge each stick before starting the discharge/charge reconditioning cycles. But before the lengthy cycling process starts, set the machine for a minimum of three discharge-charge cycles. My iMax can do up to five cycles automatically, but you don’t really need to spend that much time on each stick to sort the good from the bad. With the good sticks, more than three cycles does not necessarily make the stick perform significantly better. If a stick is somewhere “between” good and bad, then the cycling process often straightens it out nicely.

With the iMax B6, each cycle takes at least 10 hours to complete. Multiply that by 20 sticks and you can quickly see that reconditioning the entire pack will take 25 days of round-the-clock reconditioning. Try to time your “starts and stops” so that the charger alarm doesn’t wake you up in the middle of the night, though the alarm can be turned off.

The iMax B6 is made for small, radio-controlled batteries, and with light loading to keep the cells from getting too hot, the IMA conditioning process is lengthy. But it does get the job done with IMA sticks too, and it is less expensive than similar devices. Other reconditioners use much higher discharge rates and cycle faster. However, the additional heat may also cause otherwise-OK sticks to be heat-damaged.

If the stick is working right, it will feel slightly warmer than room temperature and all the cells will be the same temperature during the process. It should also charge to about 6,400 mAh when full and do it in a bit more than one hour from a minimal state of charge (0.8 V per cell). If all goes well, the final numbers in the display will be about 6,400 mAh charged, and 5,700 to 6,100 mAh discharged. If you have any sticks that vary greatly from these values, treat them with suspicion and mark them as problematic.

It is best that all the sticks in your pack discharge to about the same level. Very odd discharge characteristics in some sticks will drag down the better ones, causing the dreaded IMA warning light to come on sooner than it would otherwise. However, a 100 to 400 mAh difference will not present a significant problem to the car’s computer. None of the sticks will have exactly the same discharge value no matter what you do.

The End Result

At the end of a month of reconditioning, six bad sticks—out of the 20 in the pack—showed up, which explained a lot as to why the car functioned so poorly. Each failed stick was either excessively slow to charge or only at a partial charge after the machine said it was done. During cycling, poorly performing sticks will also get much warmer than correctly performing ones. Heat is one of the items that triggers the IMA warning light on the dashboard.

The next step was finding replacement sticks. I had to replace 30% of my battery pack and the most cost-effective way was to buy a junkyard battery pack and put it through the same charge-discharge process to find its good sticks. This took another 25 days, but was well worth the effort—the car now runs like new, gets 50 to 55 mpg on the highway again, and all the computer errors have vanished. I also have 12 good spare sticks for the next time I need to do this—probably in three to four years, judging by how long the original battery lasted before the computer errors showed up.

Failing IMA packs can also cause seemingly unrelated computer errors, like oxygen sensor failures and a 12 V battery error. The 12 V battery charges from the IMA pack through a DC-to-DC converter—my best guess is that the car’s computer uses it as a reference voltage to judge how well some of the car’s other sensors are working. In any case, all of the original error codes went away after the IMA pack was refurbished.


Michael Lamb s a professional handyman who loves tinkering with electrical things. After 10 years working at the Energy Efficiency and Renewable Energy Clearinghouse as a consultant, he retired to tinkering full-time.

Comments (44)

justevan's picture

SK or anyone
what is the best (and cheapest) way to set-up pack charge and discharge. I am a electronic tech. so I can build one. do u know of any proven ways to do so?

joncountry's picture

Does anyone know if this would work for a Toyota Prius ? Thanks.

YPATY's picture

Has anyone in the Washington, DC area tried this?

lmlisak's picture

Can someone give me the measurements of these cell sticks?

35mm x 385mm... along those lines

S K's picture

Aftermarket modules off Alibaba are:

34.0±0.5mm dia at their widest
382 ± 2mm length

I have used aftermarkets in packs, and they fit as well as the OEM, so I trust those numbers.

Curious. Why?

lmlisak's picture

I thought about buying a set of 20 from one of the Shenzhen companies... they have a 20 stick min order...
I have Chinese speaking managers where I work, so I can ask for their assist if their is a language problem.
Parameters from the vendor
Voltage: 7.2V.
Capactiy :10000mah( Original 6500mah)
Size: 35mm*384-394mm
Continue Discharge Rate: 100A
Support 50A charge rate
6 Cell per stack with both ends stainless square and hexagonal standard electric car battery nuts

So It sounds like you've done this route also...

S K's picture

No, I have not done this, BUT I have worked with one of the main battery builders for Insights/HCH1. He uses 8Ah sticks from China, and I have recently measured some for re-shrink wrapping used ones from 2012.

I would vigorously discourage you from the 10Ah version. It's an inflated/gimmicky rating. The technology doesn't exist to make the cells with that capacity in this application. The 8Ah rating is also a little gimmicky as it's not truly a capacity increase for the car, but it's a decrease in internal resistance that enables more capacity at currents well below the car's requirement. I have personally tested the 8Ah sticks at 20A discharges, and they test around 6000mAh, which is a little better than Honda.

Additionally, to give you a reference, MOST of the 20 sticks in the Insight pack from the battery builder are showing issues that will inhibit long-term trouble-free function, but will likely function well with periodic grid charging and discharging. These sticks were subjected to worst-case Arizona heat and extended periods of sitting

The effort associated with rebuilding a pack is very high. It will require minor modification if your pack still uses the PTC strips as new sticks typically don't include them and newer models don't use them.

If your IMA system has recently failed, and you still have partial function, grid charging and discharging could enable another 1-2 years of good function.

If you're still going the China route, avoid anything that looks anything like "KingKong" batteries. Their quality is very spotty. Additionally, don't expect any warranty to be honored.



lmlisak's picture

Hi Steve:
My check engine and IMA just started showing up a few days ago. I was a Bench tech for a decade, and I still dabble in my skills. so I believe I will not have a problem with the my 2007 I may be surprised when I open it up..if you say KingKong is one to avoid, I will need to be carefull buying from across the pond.
I cannot afford the retail and my thought was to just find the cell packs....
this Ali-thing doesn't support that many vendors in this type of battery... ( sigh )

S K's picture

First, get the code read. It's usually the battery, but it can be other things.

Second, check out your 12V battery (make sure you have your radio/navi codes before disconnecting). A weak 12V can trigger a marginal IMA issue. Have your 12V battery LOAD tested. If it tests at less than 80% capacity, replace it. The act of disconnecting the 12V will reset the BCM and IMA light. This will trigger a forced regen. Allow the car to idle and charge until the SoC gauge reads full. If it terminates charge before full SoC, do it again. Repeat the 12V disconnect and IMA charge to full SoC a total of 3 times (the last one usually takes under a minute). This process can often get an IMA light to go out for months. It doesn't fix it, it just improves the issue a bit and puts the light off for a while.

There are no viable Chinese replacements for 2006-2011 due to the fact they the Honda sticks are welded in pairs. Hybrid ReVolt and Bumblebee Batteries have fabricated replacement pairs from Chinese single sticks in their replacement packs, they are notably cheaper than Honda, and they come with a 3 year warranty on which you can count.

Again, I encourage you to to pursue grid charging. The HCH2 responds pretty well to them. I have 2X '06. You can build your own grid charger/discharger for about $90. Since the HCH2 fan is PWN controlled, you either need to devise a way to run it or charge/discharge with the pack out of the car. It can be done in a weekend, and you'll likely get another 1-2 years of life during which you can save for a new pack.


S K's picture

All, I vigorously encourage you to abandon stick work. It's generally a waste of time.

Chas, Per my comments below, the Turnigy Reaktor 300W. Cells should never be too hot to comfortably touch. 100-120°F is the realistic maximum. Get them hot enough, and you damage them.

Justevan, congrats on your results. Your success or failure will be determined in how long it takes before you start to recalibrate again. If it's more than 2-3 months, great. Don't expect it though. Insight G1 and HCH1 sticks almost never rejuvinate for a significant period of time due to increased IR and self-discharge of 1-2 cells in a stick.

All, I encourage you to pursue grid charging/discharging before you ever consider doing stick work. Here's a DIY BOM for a charger and a discharger:

This must be done outside the car; remove the pack and take it in the house.

The reward vs. effort of the above process is 100 times higher. You'll have about 1.5 hours total time invested, and you'll know 100% if your pack will refurb at the end, and it gives as good or better results than stick work in a single weekend with nothing more than occasional monitoring.

So, Chas, grid charge/discharge/charge the spare pack and balance them all in one shot in one weekend, eliminate 99% of the voltage depression and recover 20-25% capacity. Here's my before/after sheet:

Lastly, here's all you need to know about grid charging/discharging:

The only time you should do stick work is AFTER a pack has started to misbehave following a grid charge/discharge/charge. You can then discharge your as-removed sticks a single time and know exactly which ones are shite.


justevan's picture

Chas Seligman,
make sure after charging and discharging as S K stated below.
then do another charge, make sure it reaches at least 9.4 to 9.5V.
if not try deep charging to 4.2, just remember when discharging past 6V that u do it at 0.3A. also make sure the hybrid battery fan turns on when the battery charges. as when u slow down and stop, the fan should still run for a little. my fan was located in the trunk behind the black felt paneling

Chas Seligman's picture

Which Turnigy did you use? The Imax just doesn't seem to get it. When I nwent a couple of the sticks never got hot enough to 'not touch' just pretty warm. Did you replace yours from the spare battery pack. I've purchased a spare and went trough it again with the Imax and didn't really find any bad ones. I purchased another total balancer online and it seem to work the first couple of times but lately the IMA came back on and the 'charger system' doesn't act right.
I have two of these cars that I love (getting in excess of 40 mph on both) so I have a vested interest in figuring out how to fix this problem.
Since I have a spare battery pack I want to start on that one and get it all re-balanced or identify the bad sticks.
Thanks for all your imput!

justevan's picture

i just completed this task. it was successful! i have a Honda Civic Hybrid '04. i bought a used battery pack conditioned each rod (20). 4 were suspect. i removed my own and recond. 4. installed and passed emmisions. i used the IMAX B6 charger and the Turnigy (it is faster).
follow discharge and recharge instructions below. some sticks will be
very hot , to hot to touch. these are bad, maybe more conditioning may be required. USE FANS!!. i used a 10A 12V powersupply for both my rechargers, this will get hot too. good sticks will charge upto 9.5 to 9.6V and start to get warm around 9.3V(aprox.), but not super hot.
i also used 12AWG copper wire with screw on each end so not to damage the treads of battery with a clip

gpa2042's picture

Justevan, did you run your imax in auto recycle mode? I tried to run for 3 cycle automatically but every time when it charges 6500mAh it stops and do not start to discharge automatically and i have to start it again for discharging . I do believe the batteries are rated 6500 mAh for 05 civic hybrid but my charger just keeps charging and stops exactly at my capacity cut off set of 6500mAh. Am I missing something that is not allowing it to recycle automatically?

currentchallenged's picture

Does anyone have definitive information what to set the IMAX B6 units for to process the reconditioning? I had bought a junkyard unit and it failed after 6 months. Now I just want to try to recondition the sticks to see how many I can come up with that are good. I have seen lots of posts and pages, yet cannot find anything posted as to what actually is used.

justevan's picture

follow the comments. when u start the charging process. go to setting. then NiMh sensitivity and change it to 20 (defalt is 4).
only for the .6A charge step (will take 16 hrs), after that change setting back to default. then 1st discharge is at 1.3A. then its full
charge and discharge to 6V. below 6v u must discharge at .3A (5.4, 4.8, 4.2)/ charging and discharging inbetween .
i did this , took a month , but it does work.

justevan's picture

follow the comments. when u start the charging process. go to setting. then NiMh sensitivity and change it to 20 (defalt is 4).
only for the .6A charge step (will take 16 hrs), after that change setting back to default. then 1st discharge is at 1.3A. then its full
charge and discharge to 6V. below 6v u must discharge at .3A (5.4, 4.8, 4.2)/ charging and discharging inbetween .
i did this , took a month , but it does work.

S K's picture

Did you read any of the comments? The IMAX is completely worthless for refurbishment. It can only drain 5W of power from a stick, and it takes a week to do a pack. The car subjects these sticks to 100A. 0.8A isn't going to give you any diagnostic value whatsoever.

I recommended the Turnigy Reaktor 300W charger. It can charge 6X faster than the Imax B6 and it can discharge 4X faster natively, or it can discharge 75 times faster in regenerative mode.

What I really recommend now is that you investigate grid charging and deep pack discharging. You can do it in a weekend, and your pack will likely improve significantly. Results in the Insight community have been great.

Check out:

You are pursuing efforts that have been demonstrated to be very ineffective and represent a very large time investment with very low payoff.

EDIT: To answer your question... If you insist on pursuing...

Disable all timers and capacity safeties.
1) 1A discharge to 6.0V (1.0 V/cell)
2) 0.6A charge for 16 hours (you'll have to monitor it and restart it if it stops). You can stop before 16 hours if all six cells are comfortably warm to the touch (about 100°F).
3) 1A discharge to 0.2V
4) 0.5A discharge to 0.1V
5) 5A charge to termination. Cells should be warm or very warm but not uncomfortably so, and they should all be about the same temp (< 120°F)

The above process deep discharges the stick to wipe out any voltage depression and will restore 20-25% capacity for a given discharge. Yes, you will reverse cells. No, there is no way to damage these very robust cells from reversal at these low currents.

What you can't fix is Internal resistance and excessive self-discharge. You likely have many sticks that exhibit this condition.

The BEST way to truly diagnose bad sticks is to:

1) grid charge pack for 24 hours
2) deep discharge to < 1V using 2X 100W lightbulbs in series (yes, the whole pack down to <1V)
3) grid charge 24 hours
4) Install and run until recalibrations become excessive or you get an IMA light.
5) disconnect 12V battery, reconnect 12V battery (clears the State of Charge from the BCM)
6) start and rev car to 3500 rpm to force charge battery until battery shows full.
7) remove and discharge sticks to 6V at 10-20A loads.

Good sticks will give you >3000mAh.
Okay sticks will give you >2000mAh.
Crap sticks will almost never reach 1000mAh

Good luck,


B Styles's picture


Thanks for all the info!

I just purchased the Reaktor. What is a good power supply for this charger? The iMax chargers I currently have are the dual power AC plugs. I was using the wall plug as my power source for them but I won't be able to do that with the Reaktor.

Also, what would the best settings be to use for reconditioning the the sticks with the Reaktor charger?

Once again thanks for all your help and advice. Hopefully I will be able to recondition a decent battery pack for my HCH.


S K's picture

EDIT: I just received my Reaktors... they are NICE. Finish and interface is MUCH better than any of the Chinese knock-offs I referenced.

EDIT #2: While the 20W discharge rate isn't fantastic, it's pretty good. I've gotten accustomed to 10A and 15A discharge rates with other pricier devices. The Reaktor also has an internal resistance measurement feature, and it comes with temp probes, which I highly recommend using.

This should drive one more than sufficiently. I have 3 of these running my farm of IMAX B6, the reaktors and a iCharger 206B knock-off:

360W. I've run them at 300W for extended periods with no issues.


1 cycle at:
mAh limit, 9600 max
no time limit
Set NiMH sensitivity to 20mV, so it doesn't shut off prematurely
60 minute rest period
0.6A charge rate (will run until it reaches the 9600mAh cut off @ 16 hours)
1.3A discharge rate to 6V

For subsequent cycles:

Reset NiMH sensitivity to default
6.5A charge rate
Max discharge to 6V
Manually discharge at 0.3A to X

X shall be 5.4V, 4.8V and 4.2V for the 3 cycles. When going below 6V, do this MANUALLY at no more than 0.3A. You're driving cells down below voltage depression thresholds and causing reversals at LOW current for relatively short periods. This will not harm these robust cells. Deep discharge and reversals under low current have demonstrated substantial capacity gains.

4th time:
6.5A charge rate
Max discharge rate to 6V/stick
That will be your final capacity.

After these efforts are complete, I highly recommend you build your own grid charger for less than $75 or so.

Good luck!

S K's picture

My guess is you purchased the non-genuine SKYRC IMAX B6 for $25 each or a bit more for the AC models. I have several of these, and I have exactly the problem you describe. Some do it most of the time, some do it almost never. This problem is all too common with the Chinese knock-offs. These sellers get the same stuff from the same manufacturers. I fully believe there is a defect with these chargers.

You may get more success by pumping it up to 5.0A charge.

Lastly, the chances of you refurbing the sticks from a 2004 are very poor. At 10 years, you're looking at 10-20% deterioration from age alone. I am in the process of analyzing a pack from a 2003 (mileage unknown), and the bulk of the 6.5Ah rated sticks are coming in at 4.6-4.8A AFTER cycling.

I'd return all 4 of those chargers for a refund and place an order for a couple of these:

They have a 20W discharge capability compared to the 5W of the B6, so they can literally discharge as fast as 4 B6. If you rig 2 sticks in series, you could use the regenerative discharge to test two at a time at 20A discharge. I just purchased 2 of these, and can't wait to get them tomorrow.

Good luck,


B Styles's picture

Hello Micheal Lamb,

First I would like to tell you that your write up is excellent and I was able to remove and dismantle my hybrid battery with minimal difficulty.

However, now I'm having troubles and I figured this forum would be the best place to ask for help/advice.

I have a 2004 HCH. The IMA light has been on for a few months now and my gas mileage has went from 42 to 30 MPG, so it was time to get a new hybrid battery. After doing some research online I came across a few ways to recondition the battery myself. Using this site and your experiences as my guide, I started the steps to recondition the battery.

Since I knew I was probably going to need another hybrid battery, I bought another one off eBay for about $350, along with 6 iMax B6 chargers. I decided to take apart the spare battery and test the sticks inside first.

Now this is where I am my troubles. On the initial charge a lot of the sticks were not taking full charges that made sense. The iMax would read the charge was full in about 20 minutes and I would get reads of 29 - 410mAh.

These are my settings:

Timer - Off
mAh Limit- Set to 9600mAh
Charge - 0.6A

The weird thing was there were times when I could have 3 or 4 chargers going off at the same time with the same "full charge" reads with low mAhs (30-250mAhs). I thought maybe I had some bad iMax chargers but I bought them from 3 different sellers so I don't think that is the case. I also thought all the sticks in the spare battery were just bad but I don't think this is the case either.

I just want to know if you came across this problem when you were charging your sticks and if so what did you do to fix this?

Also, if anyone else in this forum has come across this issue please feel free to give you advice/fix. I just want to do this right the next time when I try to recondition the hybrid battery that was in my car.


S K's picture

I have done this on 4 HCH2 (2006, 2007) packs. The IMAX B6 is a poor choice as its discharge current is limited to 1.0A up to 5Watts. Testing stick pairs is not a good idea as the B6 will be limited to about 400ma discharge current and may take the better part of 15-16 hours. Single sticks are limited to 800mA, and considering that these cells are rated for 100A loads, 800mA isn't a good representation of performance in the car, but it's better than nothing.

A critical factor in stick cycling is ensuring the cells are balanced within the stick from the start. This is best accomplished with a 600mA 16 hour timed charge (controlled by setting mAh limit to 9600) for your first cycle (okay to charge pairs like this as it's faster). Discharge sticks to 0.9V/cell and then repeat twice more with 5A charge and 1A discharge cycles to 0.9V/cell. Repeat a 4th time to 1.0V/cell and consider this your final capacity from which to determine replacement or reuse.

Limiting your current isn't a good idea as charging efficiency isn't 100%. HCH2 sticks are rated at 5.5Ah or 6.0Ah depending on source. I use 6.0Ah, and when I charge with delta V cut-off criteria at 5A, the IMAX reads about 7700mAh pumped in.

This is a laborious process. I recommend the purchase of multiple non-genuine IMAX B6 from eBay (about $22 each). I have 15 of them. It's nice to be able to sort through a bunch of sticks in just a few days.

I also use a CBA III battery analyzer (CBA IV is currently in production) to discharge test the sticks at 14.5A to get a more accurate reading of their capacity at higher loads. Discharge takes only about 25 minutes, so I can do a whole pack in a day.

P.S. Regardless, nice write up of your experience.

Michael Lamb's picture

Hi Irfan ul Haq,
The answers to your good questions are as follows:
DIsable any timer limits on your iMax.
Charging the sticks first then begin cycling is a good idea.
The iMax has a 5 cycle limit, but you should get a good idea how each stick set is doing after about 3 cycles. If they are doing ok continue with 5 cycles.
The cycling Amps should be as high as the iMax will allow. I think this is 5 amps.
Doing all 12 cells at one time should not be a problem. It will just take longer than my 6 cells per stick did.
One more tip: set the charging limit at 6400 mAH. I think this is correct for you 2006 HCH. Mine was 6400 anyway. I suggest you do some additional research on that issue yourself. Set the charging limit accordingly.
Best wishes

iuhaq's picture

Dear Mr. Michael Lamb, Good Day!

After reading your article, I thought of giving it a try with my Honda Civic Hybrid 2006. I bought a battery pack from junkyard so as to keep the car running while reconditioning my battery pack.

I now have a HCH Battery pack, and have dismantled. It has 22 sticks welded together in pairs making 11 pairs. Looking at the welds, I will not be able to remove sticks from pairs therefore I thought to get the performance data of the stick pairs and remove the bad pair sticks and replace them with good one (as I have two battery packs available).

For reconditioning, i bought a new charger/discharger i.e. iMax B6 AC (Dual Power) 80W, which can charge NiMH up to 15 cells, as written on its box.

I tried charging one pair of sticks, but the charger stopped at 140 mins, and when i checked the settings, I came to know that there was a time limit defined for the charging as 140 mins, which I disabled.

The instructions which came with the charge are difficult for me to understand, therefore I am writing to you to take help to setup my charger for reconditioning the stick pairs.

My questions are as below:

1. DO I need to charge stick pairs before starting discharge/charge cycle? If yes, then what will be the settings of my charger? Current, time limit (if any) etc.
2. How many discharge/Charge cycles do i need to do to get performance of sticks so as to decipher between good and bad stick pairs.
3. What will be the settings of discharge/charge cycles i.e. Current for Discharging, current for charging, time limit to be removed?, and other settings on my charger to successfully get performance data.

Each stick has 6 cells, and a stick pair means 12 cells and as per charger specifications it can charge up to 15 NiMH cells. Therefore, I would like to do the process on stick pairs rather than individual sticks, does this make sense?

Kindly reply to me on above so i can start the reconditioning of my HCH 2006 IMA Battery Pack.

Kind Regards,

Irfan ul Haq

kilog's picture

All my congratulations for this comprehensive and wonderfull job.
Can I do the same for the RX400H lexus of my brother?
The HV Batt are down
and from here (Douala - Cameroon) in Africa there is no other solution than trying to refurbish the HV batt and start the car.

Michael Lamb's picture

Judging from what you wrote, I would have to guess that the HCH and Insight packs are similarly controlled and will likely act the same disconnected. However I would not advise doing so myself. Be careful, best of luck.

repurposedartifact's picture

It is only being driven on rural roads during daylight hours. I was concerned that there may be some sort of additional electrical problem with having the cells removed as opposed to just having the battery breaker flipped off. We have been driving our 1st gen Insight with the battery breaker off and it is totally fine performance wise for our normal use. It is important to my wife that both cars are drivable.

Michael Lamb's picture

Possibly, but like I said I never tried to do that. The closest thing I have experienced that might be like having the pack out, is me driving when my Honda HCH does a "recalibration" on its own. If I am tring to accelerate during one of those, the car is a real dog and has a hard time getting out of it's own way. During hot weather (and when the air conditioning is on) this sluggishness gets pretty hairy in traffic. If you really must operate the car in such a state, be very very careful. None of this is worth risking your life over you know.

Michael Lamb's picture

I have never tried to operate the car without the pack installed. Off hand though I would not advise doing that since it could make the car unsafe in traffic.

repurposedartifact's picture

Thanks for responding Michael. I don't know how you mean that the Insight would be unsafe with the battery sticks removed from the pack. Would this be any different than running the car with the battery cut off switch turned off when batteries are in place?

repurposedartifact's picture

Is it possible to put the battery pack back in the Insight without the battery sticks? I'd like to drive the car on just the IC engine while the batteries are conditioning over the two week period.

Michael Lamb's picture

Hi mortonarts,
The Imax comes with directions on making multiple cycles. Please be sure to read the instructions carefully. Also read the rest of the comments here for more useful tips.

mortonarts's picture

Hey all. So I bought 20 sticks of stripped batteries(No heat shrink) and I bought 2 iMax B6 chargers online. For some reason the battery tender will not do more then one cycle through. I have to switch it from discharge to charge to charge to discharge. Does anyone have better directions on how to use these chargers? Also they came in the mail with no power chargers. I used a few laptop power converters I had laying around. Any help would be great as I cant afford 3 grand on a new battery.

S K's picture

Under no circumstances should you install sticks without heat shrink into packs. This has been known to cause fires in Honda Insight battery packs. The mounting rubber is conductive enough to heat up and burn.

Chas Seligman's picture

Let's be honest about the instructions included with the iMax...they suck. I read them and reread them and couldn't make heads or tails out of them, so I just played with the buttons to get an understanding on how to work the darn thing. The best thing about the iMax is it's smart and won't let you do anything too stupid or ruin the batteries.
If I remember correctly in order to change the number of cycles the system had to be in the C/D mode with number of cycles flashing. While that number is flashing press the green button and that should increase the number of cycle the charger will cycle through.
I agree with the author that you don't need any more than three cycles because the batteries do not improve any more than during the third cycle. I tried five cycles and the difference between a five cycle charge and three cycle charge is very minimum

Michael Lamb's picture

Hi Chas
The best values for D and C are "the more the merrier." All the chargers you will find have a max D and C setting. Choose the highest one. This is far lower than the car computer will have zipping though the cells when the car is in operation so do not overly worry about the cell overheating during reconditioning. The charger will automatically keep things in a safe range. I believe many chargers also have an external temp probe you can buy just to be certain, but I did not find this expense necessary. Also if the cells get a bit too hot they are gonners anyway. A good cell will never get much over room temp if it is working correctly under load.

Michael Lamb's picture

Hi everyone! I am the author of this article and will try to answer the concerns I read here. First off though let me ask you to re-read the entire article until you recall most of it when you have a conversation with someone. Most of the questions I have seen all relate to things ALREADY outlined the the article. I really hate repeating myself so please do me that little favor. Thanks.

A couple questions I have been asked that have not been touched on are:

1) Can I use some other type of battery pack (i.e., LiPo, homemade NiMh etc) The short answer is NO!! Not just NO but "you are crazy if you do" type of NO. The reason is: Honda makes the pack in such a way that the computer actually communicates with it and if the computer doesn't like the conversation nothing works right.

2) Can I use more than one charger to speed the reconditioning up? Yes you can. Use any of the charger made for reconditioning NiMh cells, you do not necessarily have to use an IMax. I used an IMax because it came with the car when I bought it.

3) Where can I buy used sticks? The best I can say is that they are getting rare to find and the ones I have heard other people finding online and at junkyards are not a lot better than what they already own. I suggest that if you cannot find good sticks then make the best of the ones you do have by carefully reconditioning them. Do not rush the process. Chemistry is at work in the cells and believe me it doesn't like being rushed.

Chas Seligman's picture

This was a very useful article and I used it to recondition my 2004 Honda Hybrd also with the iMax that cost around $65. It took about 3 weeks to recondition all the stick and a couple of them I reconditioned to make sure they were within 10%. One question I never really figured out was what were the optimum values of the charge value (volts and amps) s well as the discharge values of the same. As another person asked and I also have searched out these numbers and could not find any information on this subject. Any insight on the optimum values would be a great help because I do not think this will be the last time I go through this process. Thanks for your time.

currentchallenged's picture

One question I keep seeing, but never seeing the answer for (and I have been searching a number of threads and sites.

When using the B6, what are the values used. From charging to discharging, voltage and configuration? I know very little about electricity and am probably not the best person to be trying this, but I am good at following directions, as long as they are in layman's terms.

I went and purchased 4 of the Imax B6 (clones most likely) and a junkyard HCH battery. I have had issues with the charging and such of my 2003 HCH but never got anywhere with it. I average 40 MPG and until I can find a replacement hybrid, I have to get this one to pass emissions.

So at the moment, I have 2 batteries, one in the car, one on a bench. I just need to start the recondition process and could use some hand holding while getting it started.

Computers I can understand, Anything that Nikola Tesla could have thought up, not so much.

S K's picture

Disable timer
set mAh limit to 9600
charge manually at 0.6A until it shuts off (about 16 hours)
discharge to 0.9V/cell at 1A (it will never read 1A, will peak at 0.8 or 0.9)

Set c/d cycles to 2
set charge rate at 5.0A
set discharge limit to 0.9V/cell
set discharge to 1A
run 2 cycles

Conduct single charge discharge per above except to 1V/cell. This is your final capacity.

Wolf Baginski's picture

This process is lengthy enough that you have to wonder if a vehicle like this is designed for a long life. Most of the total energy cost is still the manufacturing. And, from my own experience, a Honda Civic may reaching its mechanical limits after two battery packs. I'd certainly want to look closely at the rest of the vehicle, to judge how much time I could get out of it.

There are alternatives to Honda battery packs, still expensive, and this process is trading time for cash. I would consider buying more than one battery reconditioner. Spending another $55 to halve the time, if your domestic wiring is good enough, is almost a no-brainer.

I understand current models use Lithium-Ion cells. You may count me as nervous about the propects of that. Not just the reputation they have for fires, but a general feeling we don't have enough experience of the technology to feel comfortable. These machines could warp the whole used-auto market, you can see a $3000 bill on the horizon. The price ought to be lower, but will it be?

I think we are all still learning.

Michael Welch's picture

Some further info from the Author Michael Lamb:

During my HCH rebuilding ordeal I tried many different settings but found that the following worked out ok:
Set the Charging and Discharging settings to as high as the Imax will allow.
Disable the timer setting.
It is your choice to disable the alarm. I had mine "on." It would often wake me up at odd hours of the night, but I was in a hurry to get the work done so I put up with it.
The other settings the Imax has can be left on the factory defaults. They worked well enough in my opinion.
Make certain your Imax is set on "NiMh."

Yet More from the author:
A junkyard is about the only place I would find a used IMA pack. Mine cost me about $300 (noted in the article.) However I have been seeing them get a lot more expensive since there are fewer of them available as time goes on.

I sometimes see them on Ebay too, but I have heard some seriously negative things about Ebay sellers selling really messed up sticks as "working." Good luck getting your money back.

I wish you the best of luck locating used sticks (or packs) that are still worth spending money on. As these cars get older, so do the cells/sticks that are in them. Batteries do not get better with age either.

It may also be worth noting that I ended up "buying" a "cheap" Honda factory refurbished IMA pack from the Honda dealer where the car was originally purchased. This was some 20 months after the article came out. Check with whoever originally sold that car new for any deals they may be offering.

Also there is a Class Action lawsuit settlement going on right now. Look at for more details on this.

There are also a number of small claims actions around the country if you care to take your chances in a courtroom for yourself. Check out
Her case may give you some pointers on how you can proceed if you care to do as she did.

The author on a related subject:
I also sometimes like to caution owners of Honda hybrids which have a CVT transmission (which is most HCH's) to change the tranny fluid every 12,000 miles (or with each engine oil change) to avoid early transmission failure. Following Honda's service advice on the trans WILL cause the owner problems much sooner then necessary. I find lots of dead HCH transmissions in the junkyards I frequent around here. BIG money replacing a CVT! Costs more than the entire used car does currently. Search online to find some graphics that show how to change the fluid yourself (saves about $400 labor by DIY).

akvenkatesh's picture

Hello Michael L,
Can you please explain the charging amp/volt used .
When you say that the batt was discharged, was imax-b6 used to do this job.

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