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Battery Life Calculator

Work out battery life instantly with clear inputs, formula shown and shareable results.

About Battery Life Calculator

Runtime is usable capacity divided by average current. The efficiency term covers Peukert losses, converter inefficiency and the fact that rated capacity is measured at a gentle discharge rate — draw a battery hard and it delivers noticeably less than its label.

Formula

Battery runtime

hours = capacity (mAh) x efficiency / average current (mA); C rate = current / capacity

Worked example

With the default values below, Battery Life Calculator returns Runtime of 13.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Battery capacity
2,600 mAh
Average current draw
180 mA
Discharge efficiency
90 %

Results

Runtime
13.00 h
Runtime
780 min
Usable capacity
2,340.00 mAh
Discharge C rate
0.069 C

Step by step

  1. 1Values used
  2. 2Battery runtime
  3. 3Runtime= 13.00 h
  4. 4Runtime= 780 min
  5. 5Usable capacity= 2,340.00 mAh
  6. 6Discharge C rate= 0.069 C

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

What is the C rate?

Discharge current expressed as a multiple of capacity. A 2,600 mAh cell at 2.6 A is 1C. Above about 1C most chemistries lose usable capacity.

Why is average current the right figure?

Because energy, not peak power, sets runtime. Compute a duty-cycle-weighted average of active and sleep currents.

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