Battery Capacity Calculator

The load you enter is what the AC-side equipment actually consumes, but the battery only supplies DC power, which the inverter converts with some energy lost as heat in the process. To deliver a fixed amount of usable AC energy to the load, the battery has to supply more DC energy than the load number alone suggests -- so a lower inverter efficiency (more loss) means the battery must supply even more, which is why decreasing inverter efficiency increases the calculated required capacity rather than reducing it.

Depth of discharge (DoD) sets what fraction of a battery's nominal capacity you can safely use before it's considered fully discharged -- a battery rated for 80% DoD only delivers 80% of its labeled capacity as usable energy. A higher allowed DoD means more of each battery's nominal capacity counts as usable, so fewer total amp-hours or watt-hours of nominal battery capacity are needed to deliver the same amount of usable energy to the load.

No -- the required watt-hours and kilowatt-hours are driven entirely by load power, runtime, inverter efficiency, DoD, and temperature derating, none of which involve voltage. System voltage only comes into play when converting that fixed energy requirement into amp-hours (Ah = Wh / V), which is why a higher system voltage lowers the required amp-hour rating for the exact same energy requirement -- the same energy is just being delivered at higher voltage and lower current.

No -- they're general planning defaults, not a fixed spec for any particular battery chemistry. Safe depth of discharge varies substantially between battery types (commonly lower for flooded lead-acid, higher for AGM, and often much higher for lithium iron phosphate), and cold-weather capacity derating depends on both the battery chemistry and how cold your installation actually gets. Always replace these defaults with figures from your specific battery manufacturer's datasheet before sizing a real installation.