Size home battery storage for a target backup runtime on critical loads.
Nameplate capacity always exceeds deliverable energy, because neither full discharge nor lossless conversion is available. Combining the two factors typically means about 80 per cent of nameplate reaches the load. Sizing on nameplate capacity alone overstates runtime by roughly a fifth, which is the difference between lasting the night and not.
Battery Backup
Nominal capacity = load × runtime ÷ (depth of discharge × round trip efficiency)
Nominal capacity = load × runtime ÷ (depth of discharge × round trip efficiency) Nameplate capacity always exceeds deliverable energy, because neither full discharge nor lossless conversion is available. Combining the two factors typically means about 80 per cent of nameplate reaches the load.
Sizing on nameplate capacity alone overstates runtime by roughly a fifth, which is the difference between lasting the night and not.
This calculator takes 5 inputs: Critical load, Target runtime, Usable depth of discharge, Round trip efficiency, Capacity per battery module. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.