Power storage and battery maintenance. It’s half the equation of off-grid systems. The solar array may produce the power (aka wattage) that the inverter doles out incrementally to power tools and coffee makers, but without batteries to store it, it would all be for naught.

And yet it often seems that batteries are the least appreciated link in the chain from sunlight to light bulb. Probably because they bubble and belch and produce an unpleasant smell when being heavily charged. But they work hard and need all the kindness and consideration you can give them. Since the fact that they really have no way of letting you know how much they need attention. Except, perhaps to live a year or two longer than they would have otherwise.

It is a fact that the first batteries owned by a neophyte off gridder are more likely to die of ignorance (yours) or neglect than they are to live to a ripe old age. It’s the reason those of us who have been around off-grid systems for a decade or two recommend that you begin your off-grid adventure with a set of “starter” batteries, such as T-105 golf-cart batteries. They work well in most installations. They are light enough that you can move them around without the aid of a defensive lineman. As well, they’re cheap enough that you will be able to replace them with better batteries when the time comes; hopefully, wiser than when you first installed them.

Battery Placement

Flooded lead-acid (FLA) batteries—the type you add water to—are the most commonly used batteries in off-grid systems. They are typically about half the cost of maintenance-free batteries, such as AGM (Absorbed Glass Mat), in which the electrolyte is suspended within a glass matrix. Or gel type batteries that use a gelled electrolyte rather than a liquid. In addition to their lower cost, FLA batteries can produce more surge power than either AGM or gel batteries. This makes them more suitable for systems with hefty well pumps or other heavy loads. But, they do need to be pampered.

You will want to situate your battery bank indoors, if at all practical, and as close as possible to the inverter. It is in violation of the National Electric Code to place them directly under the inverter. It is considered a “serviceable component” to which a service technician should have unhindered access. Usually batteries are stored within a plywood battery box with a vent in the top through which flammable hydrogen gas can escape when the batteries are outgassing during equalization.


FLA batteries use concentrated sulfuric acid as an electrolyte. As batteries are discharged, power is liberated by a reaction of sulfuric acid with the lead and lead oxide in the batteries’ plates, creating lead sulfate. As batteries charge, the lead sulfate is converted back into sulfuric acid, a denser energy compound. In the process some of the water in the acid solution is electrolyzed into hydrogen and oxygen gases. Thus there is an unavoidable loss of water. Your most frequent and important task as a battery manager, therefore, is to keep your batteries hydrated at all times. Use only distilled water, since all other types of water contain minerals that can foul the plates.

New batteries use far less water than older batteries. So, as your battery bank matures, you will need to be more vigilant about adding water. When new, our Deka L-16 batteries could easily go for four months without being watered, but after seven years of service that’s been reduced to two months.

There are many ways to add water to a battery. I’ve tried them all. The best method I’ve discovered is to build a rack on a wall above the batteries to hold a gallon jug. By siphoning water through a small plastic hose that terminates in a length of gum rubber, you can easily pinch the end closed as you move the hose from cell to cell. Don’t overfill the batteries or you’ll have leakage and corrosion. Filling them to bottom of the fill well is sufficient.


As batteries go through cycles of charging and discharging, there is an inevitable buildup of lead sulfate on the plates. Stratification of the electrolyte also occurs over time, with acid concentrating in the bottom of the cells. To correct these problems, batteries need to be overcharged from time to time to clean the plates and stir up the electrolyte. This process is called equalization, and should be performed once a month or so, depending on how heavily your batteries are cycled.

Equalization is a one- to two-hour process, performed by the charge controller, as per your programming. It is therefore important to know the equalization voltage the battery manufacturer recommends, since it is different for every battery type.

Charging Parameters

Your charge controller is the component that assures your batteries are properly charged on a daily basis, using a three-stage process. During the bulk stage, the charge controller will charge the batteries as quickly as possible, right up to a voltage limit known as the absorption voltage. This begins the absorption stage, when the batteries are maintained at a high preset voltage for a programmable period of time, usually two hours. Once complete, a float stage begins. The batteries are maintained at a much lower voltage for another two hours or so.

As with equalization, it is important for the health of your batteries that you program the precise charging parameters for your specific battery type into the charge controller, to avoid over or under charging.

Temperature Sensors

In a perfect world, your batteries would be maintained at a constant 80 degrees F. But in the real world, that is not going to happen. Particularly if your batteries are stored in an outbuilding or a minimally heated basement. Batteries can take the cold, of course, but, as anyone who has ever tried to start a car in the dead of winter can tell you, batteries lose efficiency and power as they lose heat. This means that cold batteries need to be charged at a higher voltage than warm batteries.

Fortunately, off-grid charge controllers are programmed to deal with these temperature swings, as long as they know what the battery temperature is. So tell them, by installing an inexpensive temperature sensor that sticks to the side of one of the batteries. Just be sure to get a sensor made for your specific charge controller or you’ll have problems. This is experience talking.

Battery Maintenance

Deep-cycle solar batteries are tough. They can take a lot of punishment. But, not forever. So try not to discharge them below 50 percent of capacity, unless absolutely necessary. For optimum longevity, keep them above 70 or 80 percent of full charge, and allow them to reach full charge whenever possible. And when running large loads for extended periods of time, please, wheel out the generator. In the end, your batteries will repay you with extra service.

This article is from a previous issue of The New Pioneer Magazine. Grab your copy at

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