How do you calculate battery runtime?

Runtime (hours) = (Battery kWh × Usable DoD × Inverter Efficiency) ÷ Load kW. A 10 kWh battery at 90% DoD and 95% inverter efficiency powering a 2kW load lasts approximately 4.3 hours. Reduce load to 1kW and runtime doubles to 8.6 hours. This calculator includes an inverter-efficiency input so the runtime output reflects conversion losses instead of raw battery nameplate energy.

Does depth of discharge affect battery runtime?

Yes — it is one of the biggest factors. A 100 Ah lithium (LFP) battery at 80% DoD gives 80 Ah of usable capacity, while an AGM at 50% DoD gives only 50 Ah. The calculator applies DoD before computing runtime so you get a realistic estimate, not a theoretical maximum.

How do I calculate runtime for a window air conditioner?

A typical 5,000 BTU window AC draws around 500W running. At 80% DoD on a 200 Ah 24V battery (3.84 kWh usable), runtime would be roughly 3.84 kWh ÷ 0.5 kW = 7.7 hours — before accounting for inverter efficiency. Real-world is usually 10–15% less due to inverter losses.

Quick answer: A 10 kWh battery at 90% depth of discharge and 95% inverter efficiency powering a 2 kW load lasts about 4.3 hours; at 1 kW, it lasts about 8.6 hours.

Quick Tools

Battery Runtime Calculator

Calculate how long a battery will last at a given load. Enter battery size, depth of discharge, and load watts — get runtime in hours and minutes.

Battery capacity (kWh)

Usable battery %80%

50%Usable: 10.80 kWh100%

Inverter efficiency92%

85%Output: 9.94 kWh98%

Load (watts)

Estimated runtime

19 hr 52 min

9.94 kWh output energy ÷ 500W load

Need to model specific appliances? → Backup Hours Calculator

How we calculate battery runtime

Runtime depends on usable stored energy, the load drawing from it, and inverter conversion efficiency. Depth of discharge (DoD) determines how much of the rated capacity is actually available.

Runtime (h) = (kWh × DoD × Efficiency) ÷ Load kW

LFP lithium batteries support 90–100% DoD; lead-acid should be limited to 50% to preserve cycle life.

Frequently Asked Questions

How do you calculate battery runtime?: Runtime (hours) = (Battery kWh × Usable DoD × Inverter Efficiency) ÷ Load kW. A 10 kWh battery at 90% DoD and 95% inverter efficiency powering a 2kW load lasts approximately 4.3 hours. Reduce load to 1kW and runtime doubles to 8.6 hours. This calculator includes an inverter-efficiency input so the runtime output reflects conversion losses instead of raw battery nameplate energy.
Does depth of discharge affect battery runtime?: Yes — it is one of the biggest factors. A 100 Ah lithium (LFP) battery at 80% DoD gives 80 Ah of usable capacity, while an AGM at 50% DoD gives only 50 Ah. The calculator applies DoD before computing runtime so you get a realistic estimate, not a theoretical maximum.
How do I calculate runtime for a window air conditioner?: A typical 5,000 BTU window AC draws around 500W running. At 80% DoD on a 200 Ah 24V battery (3.84 kWh usable), runtime would be roughly 3.84 kWh ÷ 0.5 kW = 7.7 hours — before accounting for inverter efficiency. Real-world is usually 10–15% less due to inverter losses.

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Battery Runtime Calculator

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Reviewed April 2026

Methodology and source note

PowerSizing calculators use shared formulas, documented assumptions, and current planning inputs that are summarized on the methodology page. Use these tools for first-pass planning, comparison, and sanity checks, then confirm local code, pricing, utility tariff, and installer specifics before you buy equipment.