How to Calculate Battery Runtime

Direct answer

Runtime (hours) = usable kWh ÷ load (kW). For a 5.12kWh LiFePO4 pack: usable = 5.12 × 0.90 DoD = 4.6 kWh, minus 10% inverter loss ≈ 4.1 kWh delivered. At a 1kW load that is 4 hours; at 2kW, 2 hours. Match this to your outage length.

The formula

usable_kWh = rated_kWh × DoD
delivered_kWh = usable_kWh × inverter_efficiency
runtime_h = delivered_kWh ÷ load_kW

Worked example

Load	1× 5.12kWh	2× (10.24kWh)
500W	8 hr	16 hr
1kW	4 hr	8 hr
2kW	2 hr	4 hr

LiFePO4 uses 90% DoD vs lead-acid's 50%, which is why it delivers nearly double the runtime for the same labeled kWh. See the LiFePO4 vs lead-acid guide and the price guide for 48V 100Ah packs ($620-780 FOB).

Frequently asked questions

How long will a 5kWh battery run a 1kW load?

About 4.5 hours. Use: runtime = usable kWh ÷ load kW. A 5.12kWh LiFePO4 pack has 4.6 kWh usable at 90% DoD, minus 10% inverter loss. So 4.6 ÷ 1.0 × 0.9 ≈ 4.1 hours; most inverters are 90-95% efficient, giving 4-4.5 hours for a 1kW load.

Need exact runtime for your load?

Luchu Energy sizes the bank to your actual watt draw. Get a sizing quote →