Enter your battery bank size, load and chemistry to find out exactly how many hours of backup power you have.
A 10 kWh LiFePO4 battery at 80% DoD and 97% efficiency provides 7.76 kWh of usable energy. At 500 W (0.5 kW), that is 15.5 hours of runtime. AGM at 50% DoD gives only 4.25 kWh usable from the same 10 kWh bank, giving 8.5 hours at the same load.
Yes, for lead-acid batteries (Peukert effect). Discharging at 2× the normal rate reduces effective capacity by 15–25%. LiFePO4 batteries are much less affected — they can discharge at high rates with minimal capacity reduction. This calculator uses nameplate capacity and does not model Peukert losses.
Priority loads for power outages: fridge (100–150 W), lights (20–60 W LED), phone charging (10–20 W), router (10 W). Total priority load of 300 W is achievable for 24+ hours with a 10 kWh LiFePO4 system. Avoid air conditioning and electric hot water — these use 2,000–5,000 W and drain batteries in hours.