Battery Life Calculator
By Santaji GadepatilinUpdated October 27, 2026
mAh
2,000 mAhcalculated
Type in any field to change it. Press × on a value to calculate that field instead.
How to use this calculator
Enter the battery capacity (mAh), the device’s average current and a usable capacity factor. The estimated runtime is calculated.
Formula
runtime = capacity × factor ÷ current
Example
2,000 mAh at 50 mA average with 85% usable: 2,000 × 0.85 ÷ 50 = 34 hours.
Frequently asked questions
How is battery life calculated?
Runtime (hours) = capacity (mAh) ÷ current (mA), reduced by a factor for losses and the cut-off voltage.
Why use 85%?
Batteries rarely deliver their full rated capacity in practice because of temperature, ageing and voltage cut-offs.
How long will a 10,000 mAh power bank charge a phone?
Converter losses and voltage differences mean a typical power bank delivers about 60–70% of its rated mAh to a phone.