Batteries used in solar power systems can last from one to twenty years, depending on type and how they are used. Factors such as improper charging and temperature all take their toll on solar batteries.
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Solar batteries are typically deep-cycle, which allows them to discharge up to 80% before recharging. Used properly, they can last several years. Each battery is rated for a certain number of full cycles, i.e. it can be discharged then recharged a certain number of times.
According to Northern Arizona Wind & Sun, an AGM deep-cycle battery lasts four to seven years and a gelled deep cycle battery lasts two to five years. A regular deep cycle battery lasts four to eight years.
Less common options are industrial batteries. Premium deep cycle batteries may last 7 to 15 years, industrial type batteries may last 10 to 20 years and surplus telephone (float) batteries can last 2 to 20 years.
The lifespan of batteries can be greatly reduced by abuse. Lifespan is reduced by storing batteries in temperatures over 77C, because they discharge more quickly. Overcharging is also an easy way to kill batteries.
Battery life can be extended by fully discharging them before recharging, i.e using them as designed. Keeping the batteries at a steady temperature, neither overcharging nor excessively draining them, all help.