A watt-hour rating alone is not a runtime. Tell the calculator the constant load and what portion of rated energy you expect to use, then enter the conversion efficiency for that same load path.

Formula: hours = rated Wh × usable share × output efficiency ÷ constant output W

Worked example

A 1,200 Wh rating at 80% usable energy and 90% output efficiency leaves 864 Wh at the load. At a steady 100 W, that is 8.64 hours.

Keep the power boundary consistent

Enter load watts on the output side of the conversion whose efficiency you supplied. For an AC appliance through an inverter, use an efficiency for that inverter and load; do not apply a second loss factor already included in a measured battery-side load. Victron’s battery sizing guidance includes appliance power and inverter losses when estimating needs.

Why the real duration may differ

Ratings depend on test conditions. Battery voltage, discharge rate, temperature, age, inverter standby draw and load cycling can change the result. This is a simple constant-power estimate, not a guarantee. If you only know Ah, the amp-hours-to-watt-hours calculator can first convert a matching nominal voltage and Ah rating to nominal Wh.

No electrical design verdict

The result says nothing about wiring, current rating, fusing, charging or whether a device can safely run on the battery. Use product specifications for those decisions. The inputs are calculated locally and are not stored.

Explore the related calculation

For a different starting point, try the Ah to Wh calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

www.victronenergy.com reference

Found a problem? Email contact@wattstoamps.app.

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