Choosing the Best Batteries

Whether you need batteries to store energy for your off-grid home, or you want backup power to keep the lights on when the grid goes down, understanding the different battery specifications will help you select the ideal batteries for your application.

To choose the right battery, you first need to know what you are trying to accomplish. What system type are you working with—off-grid or grid-tied? Where will the battery bank be located? How much maintenance are you prepared to do? And how often (or not) do you want to replace your batteries? The answers to these questions will dictate which batteries make the most sense for your renewable energy system.

Budget also plays a big role in which batteries you choose. Buying batteries is a long-term investment, and skimping on these important components can cripple a system. Getting it right the first time will pay off in performance and longevity. However, simply buying the most expensive battery does not ensure you are meeting the needs of your renewable energy system. For your system to operate and perform well, it is crucial to understand the various battery specifications and how they relate to RE system design.

Batteries used in an RE system can be broken down into two basic categories: heavy duty/commercial and industrial. A common heavy duty/commercial-type battery bank may be comprised of several 6 V, 390 AH (L-16 type) batteries. An industrial battery pack will usually be large 2 V cells (with thicker lead plates) pre-wired to 12, 24, or 48 V and encased in a large metal housing. You will pay more for the industrial battery bank than you will for the equivalent battery pack made of heavy duty/commercial batteries, but you gain longer battery life and a better warranty. 

If you are working with an installing dealer, they often have preferences about which batteries they will use. For example, some installers will only work with L-16 type batteries because they are the largest that they can readily move by themselves—each L-16 battery weighs around 120 pounds, whereas industrial batteries can weigh thousands of pounds, making them difficult to maneuver without disassembly. If you have no experience with batteries, shorter-lived, less-expensive batteries may be a better choice to get you up to speed with battery operation. But some installers will still lean toward the expensive industrial battery packs because they want to minimize battery replacement. This can be especially beneficial in an off-grid setting where just getting to the site may be difficult—much less moving the old batteries out, getting the new ones in, and having to haul the old ones away for recycling. However, industrial batteries are only a wise investment if you are confident in your ability to maintain the battery bank.

Using This Guide

This guide lists specifications for different lead-acid batteries, the most common chemistry used in RE systems. Exotic technologies such as lithium ion, liquid pocket plate nickel cadmium, nickel iron, and nickel metal hydride batteries are not included here because they are either unavailable or too costly for consideration. Get familiar with battery terms and definitions; they’ll give you an understanding of each spec’s relevance to designing an optimal battery system.

Choosing Your Batteries

As with any RE system investment, your best bet will be to identify your true needs and design a system around them. Grid-tied battery backup systems generally use low-capacity  banks made up of sealed, non-industrial batteries that will meet your needs for running critical loads like refrigeration and lighting during power outages. They are generally designed to stay at float most of the time with only occasional cycling, and are often made with calcium alloyed with the lead which helps lower battery self-discharge losses.