While batteries come in a tremendous range of types and sizes, the primary (and most important) designation is their intended use: daily cycle service or standby service. This is precisely why car batteries shouldn’t be used for renewable energy system storage. Batteries categorized as deep cycle are specifically designed to repeatedly discharge up to 80% of their power capacity, making them the wise choice for “off grid” power systems. Deep cycle batteries can included sealed and flooded lead-acid types, as well as the more modern lithium-ion and sodium-ion types.
While these batteries are designed for deep cycling, most designs of this type will have a longer lifespan if used in shallower cycles. Alternatively standby power batteries are preferred for grid-based systems with battery backups, as they are designed to supply power loads only occasionally. Built to supply large loads of energy in critical moments – like power outages – these batteries stay at full charge most of the time, and require very little energy to maintain such a charge.
Standby power batteries will have a limited lifespan when discharged frequently, but if kept in float conditions, can see significant longevity. Because of their low cost to produce, low rate of self-discharge, and lack of maintenance required, AGM batteries are the most typically used for standby power.