SOLAR · CALCULATOR

Battery life calculator

Free battery life calculator: get estimated runtime from battery capacity, load current, usable capacity and efficiency. With the formula shown.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Battery capacity

Load current

Usable capacity

Efficiency

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

t = Ah × usable fraction × efficiency / I

No Peukert effect, temperature degradation or inverter idle draw.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Battery capacity: 100 Ah · Load current: 5 A · Usable capacity: 80 % · Efficiency: 90 %

Estimated runtime: 14.4 h

This example uses the stated inputs; results for the entered values appear above.

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Estimating and invoicing tool

Ampxa is developing an estimating and invoicing application for electrical contractors. The list below receives notice when it opens.