Choosing the Best Batteries: Page 5 of 5

2009 Battery Specifications Guide
Beginner

Inside this Article

Most battery manufacturers have a full line of products.
Most battery manufacturers have a full line of products in different amp-hour capacities and voltages.
A classic Trojan L-16H flooded lead-acid battery
A classic Trojan L-16H flooded lead-acid battery—420 AH at 6 V.
Golf cart batteries
Golf cart batteries are inexpensive but shorter-lived than industrial batteries. They can be good “starter” batteries for people new to battery use and maintenance.
Surrette industrial battery
Some large, industrial batteries, like this Surrette model, come in single 2 V cells.
A Hup industrial battery from Northwest Energy Storage
This Hup industrial battery from Northwest Energy Storage demonstrates how single cells are contained in protective steel cases.
Bogart Engineering Tri‑Metric AH meter
An AH meter like the Bogart Engineering Tri‑Metric is an important tool for monitoring battery state-of-charge.
A single 2 V FLA cell, in a protective steel case.
A single 2 V FLA cell, in a protective steel case.
A Sealed FullRiver AGM Battery
A sealed FullRiver, similar in dimensions and capacity to a flooded L-16.
Concorde’s Sun‑Xtender AGM battery
Concorde’s popular Sun‑Xtender battery is about the same size as an automotive starting battery.
Sealed batteries installed on their sides
Sealed batteries can be installed on their sides to limit the amount of space required.
Most battery manufacturers have a full line of products.
A classic Trojan L-16H flooded lead-acid battery
Golf cart batteries
Surrette industrial battery
A Hup industrial battery from Northwest Energy Storage
Bogart Engineering Tri‑Metric AH meter
A single 2 V FLA cell, in a protective steel case.
A Sealed FullRiver AGM Battery
Concorde’s Sun‑Xtender AGM battery
Sealed batteries installed on their sides

Equalization Charge Set Point Voltage. An equalizing charge cycle is a controlled overcharging of the battery bank to make sure all cells get charged, and to remove sulfate ion bonds on the batteries’ plates and to regain battery capacity—before permanent bonds develop. First, the battery is charged to full capacity by completing a bulk and absorption charge cycle. Then the battery is charged for an extended period of time, typically 6 to 12 hours, at a C/20 rate (charging amps equal to battery’s AH capacity divided by 20). By controlling the charge rate at C/20, the battery is kept from harm. (Uncontrolled overcharging can warp the batteries’ plates, causing it to short out and possibly explode.)

Equalizing an FLA battery is essential to maintaining battery life, but can be difficult to achieve with the limited current available from a PV array. In off-grid applications, a backup engine generator is often used to equalize the batteries through a charger. Off grid, the use of household loads is generally limited during equalization to make sure enough current is available. In utility-tied systems with batteries, the grid substitutes for a generator.

Using the example of the four-battery bank (6 V each, wired in series for 24 V) and an equalization charge set point voltage range between 2.5 and 2.67 V per cell, the ideal battery bank equalization charge voltage set point for this particular battery bank would be between 30 and 32.04 V.

It is commonly believed that sealed batteries should never be equalized, yet some sealed battery manufacturers will provide an equalization voltage set point for their batteries. It is important to note that these values are usually the same as the bulk voltage set point for that battery. Typically, equalizing sealed batteries means merely extending the absorption period for a longer duration than normal. Additionally, sealed battery “equalization” is usually done only if the battery is showing signs of premature capacity loss (i.e., not lasting as long as normal on a charge), and is not part of routine battery maintenance. Regardless, equalization is very battery specific, so it is important to find appropriate voltage set points and charge current ranges for your particular batteries.

Dimensions. When you’re designing your battery bank, the size of the batteries—their length, width, and height—determines the size of the containment that you’ll need to buy or build. In addition to considering the dimensions of the  batteries, it’s a good idea to leave 1/2 to 1 inch of space between each battery. This will help keep the individual batteries operating at the same temperature and allow them to shed heat during heavy charging regimes.

Weight. Even the smallest batteries used in RE systems can weigh as much as a Labrador retriever—50 to 60 pounds. The really big batteries can weigh as much as a small horse. So, adequate trucks, skids, pallet jacks, and forklifts all become more important in moving batteries safely as the bank grows in size. You’ll need to make sure your floor and/or rack is stout enough to support the total weight of the bank.

Warranty. Manufacturers generally guarantee their products to be free of defects and perform as specified for a set period of time, and will replace defective units during this time period. Many manufacturers offer one-year free replacement with additional prorated warranties for two or three years. During this period, the distributor will replace the failed unit for a percentage of the replacement cost.

Access

Batteries have enabled Christopher LaForge to live and work for more than 20 years at his off-grid, sun- and wind–powered homestead, SunFarm, in Bayfield County, Wisconsin. He is an ISP-affiliated PV instructor with the MREA, a NABCEP‑certified PV installer, and a member of the NABCEP board of directors.

Comments (3)

Thrush's picture

Have you heard that lead acid batteries must be kept within 20% of full charge for longevity? Have you heard that Nickel Iron batteries are not significantly damaged by freezing, full discharge, and are tolerant of over charge? Redundancy on a remote homestead is desirable. Natural progression of a system is inevitable and in our case with better batteries, more water pumping, refrigeration, additional solar panels, more summer cooling, misting, etc I discovered this advantage which is not listed in any literature I've seen. It is natural with increased consumption that a 24 V system would parallel a 12V system, and maybe in the future even move to a 48V system. But the important part is that voltage bracketing of lead acids with alkaline cells (they have a wider voltage range) works really well. As a ham radio operator, maintaining the 13.5 volts for radios is much easier. As a reminder, don't strike an arc about any cell that is gassing or one might explode a cell. :-)

Thrush's picture

If you have a 12V lead acid bank of batteries, in another room or area you can place a 24V Nickel Iron bank to 'piggy back' and maintain the quality of the lead acid bank. Just tap off from the 24V bank what you need to keep the lead acids at 12.6 V. When the Nickel Iron bank reaches a full charge and the lead acids are also charged add a diversion load like a well pump or hot water heater element to th 24v bank. Having both 12v and 24v inverters add redundancy. When running short of power on a cloudy day add in extra panels and throw all the power into the 12v bank :-)

Michael Welch's picture

Hi Thrush. I guess I do not understand why one would want to do this. It sounds expensive and a hassle. There's a lot to be said for keeping things simple and straightforward.

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