Battery System Maintenance and Repair: Page 4 of 4


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Battery System Maintenance and Repair
Regular care of your renewable energy system’s batteries will help ensure that they can provide years of high performance.
Add distilled water to the batteries
Add distilled water to the batteries to about 1/4 inch below the bottom of the fill tube. Always wear eye and skin protection.
Corrosion between a battery terminal and the metal frame of a battery rack creates a potential path for current, which could create a ground fault or shock hazard.
Excessively corroded battery connections
Excessively corroded battery connections can have enough resistance to affect a battery’s performance, both when charging and discharging, and result in reducing a battery’s performance and life.
Clean all battery terminals and cable lugs
Take the time to make all battery terminals and cable lugs clean and bright before connecting the cables.
Petroleum jelly can protect terminals against corrosion
Petroleum jelly can protect terminals against corrosion, but also may attract dirt and makes using a wrench on them messy.
Always use insulated tools when working with batteries
Accidental short-circuiting between battery terminals can damage a battery and result in severe injury—always use insulated tools when working with batteries.
A battery meter
A battery meter is crucial to monitoring your battery bank’s electrical state.
Keep good records
Keeping good records is part of good battery maintenance, and can help you identify trends and spot problems if they occur.
Overcharging can result in excess gassing
Overcharging can result in excess gassing and loss of water. Exposed plates will oxidize and the battery will be permanently damaged.
Undercharging can result in electrolyte stratification
Undercharging can result in electrolyte stratification and/or sulfation (shown) and a damaged battery.
Battery System Maintenance and Repair
Add distilled water to the batteries
Excessively corroded battery connections
Clean all battery terminals and cable lugs
Petroleum jelly can protect terminals against corrosion
Always use insulated tools when working with batteries
A battery meter
Keep good records
Overcharging can result in excess gassing
Undercharging can result in electrolyte stratification

Battery Temperature Sensor­—Each month, visually inspect the battery temperature sensor (BTS), its cable, and its connection to the inverter:

  • Check the adhesion of the sensor on the battery case.
  • Verify that the sensor is in the proper place on the battery’s side.
  • Verify that the sensor is in an interior location in the pack or enclosure.
  • Check for breaks, nicks, or tears in the cable from the BTS to the point of connection at the inverter or charge controller.
  • Make sure the BTS cable’s inverter connection is not damaged or corroded, and that its protective insulation is still intact.
  • Verify that there’s no dust, dirt, corrosion, or insects in the BTS’s connector at the inverter.
  • Verify that the BTS is connected to the correct inverter.
  • Verify a reasonable battery temperature is displayed, based on ambient or battery temperature.

Common Battery Problems & Solutions

The battery bank has a mixture of strong and weak individual batteries, and is close to the end of its life. Group the strong batteries in one string and group the weak batteries in another string. This will ensure a more even charging and will allow the strong batteries to contribute more when the system is discharging.

One cell or battery has a low voltage and a low specific gravity. Remove that cell or battery and charge it separately using a power supply or battery charger. Another option is to equalize the entire bank, but this may require too much time and can put a lot of stress on the good cells in the battery.

A battery is requiring frequent watering. When there is a failing battery or cell, the “good” cells in the battery string will become overcharged and will often require more frequent watering compared to the rest of the battery. The damaged cells cause the other good cells in the battery to be overcharged. Investigate the entire battery bank to identify which cells are having problems.

One failed cell. If the battery bank is in good overall condition (verified with voltage, specific gravity, and load testing) and is less than two years old, replacing just the failed cell or battery can be a viable option. Be sure to fully charge the new cell or battery before adding it, and check all of the cells frequently to ensure that there is not a problem with the new cell or battery becoming out of balance with the others. In an older battery, a failed cell or battery indicates that the entire battery is at the end of its life and needs to be completely replaced.

Poor crimps on cable lugs or loose connections on battery terminals. Loose connections or poor crimps on cable lugs will cause high resistance. This causes the battery’s voltage to appear higher when recharging, resulting in the charger shutting off before the battery is at a 100% full level. It will also cause the voltage to appear lower when the battery is discharging, resulting in the inverter shutting off earlier than it should when running loads. Check that all the cable lugs are properly crimped and that all the connections are tight.


Carol Weis is a NABCEP-certified PV installer and ISPQ Master PV trainer. She writes curricula and teaches national and international PV classes to technicians and end users. She has worked as a licensed electrician and solar installer in Colorado, and was part of Solar Energy International’s PV technical team for 15 years.

Christopher Freitas is an engineer and project manager for international RE projects. He was a cofounder of OutBack Power Systems and was the director of engineering at Trace Engineering.

Comments (10)

cliffgrimes's picture

I have a battery bank where one of the batteries appears to have a bad cell. The SG is low and the voltage across the battery is only 4.2v, these are 6v Trojan L16s. The rest of the batteries are in good shape - SG is good and voltage levels are consistent. I am going to replace the bad battery with a new one, fully charged. My question is, after I do that is there anything I should do for the entire battery bank?

Michael Welch's picture

Have you tried a full, 8-hr. equalization on the battery bank as it is? The cell may be weak, but without occasional equalization it will steadily get worse and worse.

If you end up replacing the battery, use the bank a few cycles as a break-in then go ahead and perform a full equalization on the bank. That will bring the older batteries up as close as possible to the level of the new battery. But if your battery has multiple strings, the bank will never be better than the lowest-performing string, even with a new battery within one of the strings.

Marsha Robison's picture

I hear you Eric. But I am in a very harsh environment. Temps range from 0 in the Winter to 109 (sometimes) in the Summer. One day can have ranges of 70 degrees. My battery banks just don't preform as expected, even with diligent maintenance.
Please let me know your expert opinion on the Lithium as an alternative. I have been watching this technology but want to wait till it is perfected. Are there any other options.

Ed Mahoney's picture

I've supplied thousands of systems thoughout the world; many in extreme temperature environments. Your problem is not unique.
In high temperatures batteries will suffer extreme loss of useful life and in cold temperatures their capacity is diminished.
If the air temperature canot be controlled the best method of solving the high & low temperature extremes is to BURY the batteries in a container. Getting the batteries a couple of feet undergroung will minimize the temperature effects. You can reduce the battery's temperature by 25 F. in hot summer months and increase it by 25 F. in cold winter months.
In addition, use a battery temperature compensated charge regulator to optimize the charging voltage.
By doing this your battery will last at least 50% longer and help provide it's maximum capacity.
If you need further assistance please let me know.
Ed Mahoney

eric roberts's picture

Hi Just a point to Jim and Elaine stack? Lithium batteries have no history yet? we do not even know how to dispose of them yet, they can be highly toxic and a fire hazard, but i understand what you mean about, lead acid batteries, which are incidentally 95% recycled now. thanks eric roberts

Jim and Elaine Stack's picture

Use lithium batteries and you never need to water, they last much longer and are non hazardous. It's the 21st century and we have taken lead out of paint and even gasoline so don't use it.
Just mining it kills us. People say it gets recycles but that is a poor excuse since it gets in the air and everyplace. LEAD is one of the worst containments ever used.
Solar City used Tesla Lithium batteries for backup. Tesla is building a new battery factory that will make them 30% better or more in a few years. Invest in the future not the past.

Paul Hancock_2's picture

Great article!

I was recently moving my inverter and inadvertantly the pos and neg battery leads touched momentarily causing some sparking while they were on the ground. I know this is not good for the battery bank (I have 12 surrettee S-530s) but is there any specific way I can test the batteries to see if they sufferred any permanent damage?

Michael Welch's picture

Hi Paul. Just minor quick sparks? Should not have affected the batteries at all.

Paul Hancock_2's picture

Thanks for the reply Micheal. The sparking was just for a second or so but did melt a bit of the copper connector on the end of the cable. Batteries seem to be performing as usual but would you recommend any maintenance or testing I should be doing after this incident?

Thanks again.

Michael Welch's picture

Just go ahead and use your batteries. Rest easy, you have not harmed them.

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