Electronics
Battery life calculator
Capacity (mAh) and current draw (mA) → estimated runtime in hours.
- Instant
- Free
- Private (processed locally)
- No sign-up
Estimate battery runtime
Enter the capacity (mAh), the current draw (mA) and an efficiency. The tool estimates the duration in hours, then in days.
The formula
- Hours = capacity ÷ draw × efficiency
- Capacity and draw in matching units
- Efficiency ~85% for losses
- Days = hours ÷ 24
Example
| Input | Value |
|---|---|
| Capacity | 2000 mAh |
| Draw | 100 mA |
| Efficiency | 85% |
| Runtime | 17 h |
Indicative estimate. 100% local calculation.
Frequently asked questions
How do I estimate runtime?
Hours = capacity (mAh) ÷ draw (mA) × efficiency. E.g. 2000 ÷ 100 × 0.85 = 17 h.
Why an efficiency factor?
In practice you cannot extract 100% of the capacity: conversion losses, dropping voltage, temperature. ~85% is a cautious value.
What are mAh?
Milliampere-hours measure capacity: 1000 mAh = 1 Ah. A 1 Ah battery theoretically supplies 1 A for 1 hour.
How much does my device draw?
Draw varies with usage. Use an average value, or measure with a multimeter / USB power meter.