Battery care is your main responsibility with homemade electricity for off grid power systems. This is the one part of your power system likely to be harmed by neglect or misuse. Lead-acid batteries, the standard in home energy, should not discharge more than 50%. Ideally, they should be recharged to 100% promptly. They can be damaged by undercharging, continued overcharging, or contamination. Do not store batteries without periodic recharging. Continual self-discharge when not in use can ruin even a brand new set of batteries.

Sizing of 1000 to 2000 amp-hour 12 volt (or 1/2 that in 24 volt; 1/4 that in 48 volt) battery bank is desirable because a larger bank can accept faster charging by generator and give high power discharge for inverter surge without strain. In northern areas short on winter sunshine, more reserve before running down to the 50% level is also a benefit. Use our catalog’s 6 introductory examples as a guide to battery size, or call for advice. In sunny southwest, less battery capacity is needed.

Deep cycle lead acid batteries have thicker plates and lead-antimony support grids for years of over 50% deep cycle charge and discharge. Golf cart batteries and the “L-16” industrial batteries are the most common. Surplus industrial batteries may be deep cycle lead-antimony, or pure lead, or may be shallow cycle lead calcium construction.

Auto batteries are shallow cycle only. Cat, automobile, and truck batteries are NOT deep cycle and will not last long in home power systems. These have thinner plates and lead-calcium grids designed for less than 20% discharge and immediate recharge. If an industrial lead-calcium battery is well oversized so that normal cycling uses only the top 20% of battery capacity, lead calcium cells can be used.

RV/MARINE This common 12 volt battery is designed about half way between a deep cycle and a shallow cycle, and has medium length of life.

SEALED BATTERIES Gel or AGM (absorbed glass mat) types damage easily from overcharge, and so should be used with a 3 stage charge control. Sealed batteries can be excellent deep cycle alternative energy batteries, cleaner and safer, but only if charging is precisely controlled. Since water cannot be replaced and hydrometer testing is not possible, they are considered special purpose batteries.