Off-grid Battery Banks
listed in order of suitability to remote power use, in our humble opinion
- Industrial forklift batteries. These are truly top-of-the-line for a remote home, if you can afford them. Highly recommended for their longevity and resistance to abuse. Available in single 2-volt cells or trays of 3 cells (6 volts). 15-25+ year life expectancy. Advantages: longest life, most resistant to deep-discharge abuse, durable metal case, interconnect wires built-in, available in many capacities. Best value for the dollar when factored over service life. Disadvantages: Very high initial cost, extremely heavy.
- Deep-cycle solar batteries (L-16s). The most common choice for remote power systems. Originally designed for industrial floor sweepers, but very well-suited to remote power use. 6-volt batteries. 5-6 year life expectancy. Advantages: good service life, fairly resistant to occasional abuse, reasonable cost. Disadvantages: not as resistant to abuse as industrial cells.
- Golf cart batteries. Often used in small systems or as "training batteries" for flatlanders who move to the mountains. But don't expect more than 2 or 3 years from them if your system gets frequent or heavy use. 6-volt batteries. 2-3 year life expectancy. Advantages: very low cost, available at many discount stores, lightweight. Disadvantages: short service life, vulnerable to deep-discharge abuse.
- Solar gel cells. Expensive, but good for certain specialized applications such as on boats, RVs, and computer backup power supplies. 6-volt batteries. 2-3 year life expectancy. Advantages: maintenance-free, no hydrogen emmisions, low self-discharge rate, shock-resistant, spill-proof, cold and heat resistant. Disadvantages: expensive, requires special charger and regulator, vulnerable to abuse, life expectancy very short for the price.
- Telephone cells. Manufactured with lead-calcium instead of the lead-antimony compound of normal batteries. Not really designed for remote power use, but often available at surplus/salvage for very low cost. Can give extremely long service if pampered and not abused. Keep careful track of your battery bank's state of charge with an amp-hour meter and only shallow-cycle the batteries or they will expire quickly. 2-volt cells. Advantages: extremely low cost (sometimes even free), very low maintenance, can take very heavy use if not deep cycled. Disadvantages: cannot be deep-cycled without damage, very heavy, usually only available used, so condition is unknown, lower voltage than lead-antimony cells for charging, equalization, and metering, battery bank must have more capacity to avoid deep-cycling.
- RV/marine batteries. Very low cost with a very short life, but better than a car battery. 12-volt battery. 6 month to 1 year life expectancy. Advantages: very low cost, lightweight, available at any hardware store. Disadvantages: short life, will not tolerate abuse.
- Car batteries. Better than reading by kerosene or candle light, but will last a few months at best.
These batteries are super-expensive and hard to find unless you come across a surplus deal. They are very sensitive to damage from deep discharging, though a myth has circulated for years that NiCads should be deep-cycled. It's not true, even for AA-size batteries! They do, however, have some unique properties that are worth mentioning, since surplus NiCads do become available on occasion.
Industrial NiCad cells do not exhibit a "memory effect" like their smaller AA, C and D brethren. Both appear to "die quickly," but this is really just a function of their power curve--NiCads release power at a constant voltage until they are almost empty, then quickly taper off into nothing. Therefore, voltage readings are useless in determining state of charge. They can freeze without damage, and require different regulator and charger settings than lead-acid batteries. NiCad batteries of different ages and capacities can be mixed, which does not work with lead-acid cells.
Advantages: very long life if not deep-cycled, can freeze without damage, different sizes and ages of battery can be mixed.
Disadvantages: Expensive, voltmeter cannot be used for measuring state of charge, cannot mix with lead-acid batteries, special charger and regulator required.