Choosing the Best Batteries: Page 2 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

To properly size a backup battery bank, compute your critical load profile to determine daily watt-hour consumption during power outages. That number can often be your guide for the correct battery size. Most grid outages are less than one day, and a battery bank sized to be discharged to 50% of capacity by the critical load profile will meet most needs nicely.

If you’re off grid and rely on your batteries to meet all your electrical loads, buy a long-lived battery and be prepared to maintain it well. These systems—which cycle the batteries daily—use batteries with a lead-antimony alloy, which performs better under conditions of regular cycling. 

Typically, off-grid battery banks are sized by considering the required “autonomy”—the number of days that the battery will provide for the loads before reaching 50% depth of discharge (DOD). Off-grid systems usually size a bank to provide two to four days of autonomy. For example, if your load profile requires 5,000 WH per day, you’ll want a battery that stores 10,000 WH to achieve one day of autonomy. Four days of autonomy would require a 40,000 WH battery capacity.

Off-grid system designer opinions on maximum DOD vary widely. Some prefer to keep the depth no greater than 20%, while others have no fear of going below 50%. The deeper the regular discharge, the fewer cycles a battery will give you before needing replacement. So if you do not mind swapping your battery bank more often, go with a deeper discharge—it will save you money up front. But if swapping batteries into and out of your system is a royal pain, you might prefer maximizing battery life by buying a higher-capacity battery. For the design choice that will save you money in the long run, calculate the savings from buying fewer batteries up front, plus the cost of more frequent battery replacement (higher DOD)—versus more batteries up front, with fewer replacements (lower DOD).

...And Don’t Forget

To maximize battery life, batteries need to be properly maintained by:

• Making sure the batteries get completely recharged at least once a week by RE generation and/or supplemented with backup generator or grid charging

  • Monitoring the electrolyte and adding distilled water when needed if flooded batteries are used
  • Keeping the terminals and interconnections clean by removing built-up corrosion and keeping the battery tops clean and dry
  • Equalizing the batteries four to six times a year to remove surface sulfation from the lead plates

Specs Definitions

Manufacturer. Battery manufacturers build batteries for many different applications. Historically, RE systems used batteries originally designed for other applications, such as powering electric golf carts. Today, many battery manufacturers list which of their batteries are appropriate for RE systems. All battery manufacturer Web sites listed in this guide, with the exception of FullRiver Battery, list batteries specifically for use in RE systems.

Model name. These letters and numbers are used by the battery manufacturer to “name” a group of batteries that have similar characteristics, and distinguish them from the company’s other battery lines. It is important to not use batteries with differing model numbers within the same battery bank, as mixing different battery types can create an imbalance within the pack which leads to poor system performance and may cause premature battery bank failure. 

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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