Energy fundamentals

Battery Usable Capacity and Depth of Discharge

Understand why nominal battery capacity is not all available for routine use.

The essential idea

Nominal capacity describes the rated energy or charge under stated test conditions. Usable capacity is the portion available within the system’s operating limits.

How to apply it

Depth of discharge is the fraction removed from a full battery. An 80% planning DoD leaves 20% unused, but the suitable limit depends on chemistry, battery management, temperature, load, and manufacturer guidance.

A practical decision

Keep DoD adjustable rather than treating one percentage as universal.

Use this in a calculator

Browse all home energy calculators and replace the examples with measured or manufacturer-provided values.

Last reviewed: August 6, 2026