Home Battery
How Long Can a Home Battery Run Your Essentials?
A practical guide to usable capacity, steady loads, surge loads, and why comfort appliances change the math.
Quick takeaways
- Usable battery capacity is lower than headline capacity.
- Small always-on loads add up over multi-day outages.
- HVAC should be planned separately from basic essentials.
Start with usable energy
A battery advertised as 13.5 kWh may not deliver every watt-hour to your appliances. Inverter losses, reserve settings, temperature, and battery health all reduce usable output. For early planning, assume a usable range near 85% to 92% unless the manufacturer gives a clearer number.
Separate essentials from comfort loads
A refrigerator, modem, router, lights, phone chargers, and a few medical devices can often run for many hours on one battery. Central air conditioning, electric resistance heat, electric dryers, and ovens can drain the same battery quickly.
Runtime is a planning tool
Use the calculator result to decide what should stay powered before speaking with an installer. The clearest backup plans name the exact circuits, not just a total battery size.