Home Backup Battery Calculators

Home battery backup systems provide electrical independence during grid outages. Unlike grid-tied solar alone, which shuts down when the grid fails, a battery-backed system can seamlessly transition to island mode, keeping your critical loads running without interruption.

The foundation of any home backup system is proper load analysis. You need to identify which appliances and circuits are essential during an outage, determine their power consumption, and size the battery to cover these loads for your desired backup duration. A household backing up only a refrigerator, internet router, and a few lights draws roughly 500–800 watts. Adding a well pump, medical equipment, or a mini-split can push the load to 2–4 kW.

Battery chemistry selection affects both the usable capacity and the system cost. Lithium Iron Phosphate (LiFePO4) batteries can be discharged to 80–90% DoD daily, meaning a 10 kWh battery delivers 8–9 kWh of usable energy. Lead-acid batteries are limited to 50% DoD, so the same 10 kWh rated bank only provides 5 kWh of usable energy. This makes lithium batteries more cost-effective per usable kilowatt-hour despite their higher upfront price.

System voltage is another critical design decision. 12V systems work for small backup setups under 2 kW. 24V systems handle moderate loads up to 5 kW efficiently. 48V systems are standard for whole-house backup, reducing current draw and allowing thinner, less expensive wiring. Our calculators help you evaluate each configuration option.