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Key Features
Instant Calculation
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A battery's capacity (in milliamp-hours) and how much current your device draws together determine roughly how long it'll run. This calculator estimates that runtime, with an optional efficiency factor to account for real-world losses.
How it works
Enter the battery's capacity in mAh, the load current in mA, and optionally an efficiency percentage (below 100% accounts for factors like voltage sag, temperature, and non-ideal discharge behavior). The calculator applies Life = (Capacity × Efficiency) ÷ Current.
- Enter battery capacity (mAh).
- Enter load current draw (mA).
- Enter efficiency factor (%, optional — accounts for real-world losses).
- Click Calculate to see your results.
Examples
A simple runtime estimate
A 2000 mAh battery powering a 500 mA load lasts about 4 hours at 100% theoretical efficiency — real-world runtime is often somewhat shorter due to factors this idealized calculation doesn't fully capture.
Who should use it
- Estimating device runtime for portable electronics projects.
- Comparing battery options for a given expected load.
Industry applications
- Consumer electronics and embedded systems design
- Portable and battery-powered device engineering
Advantages
- Quick, simple runtime estimate from basic battery and load specifications.
- Optional efficiency factor for a more realistic result.
Limitations
- Assumes constant current draw — doesn't model variable or intermittent loads directly.
Common mistakes to avoid
- Assuming 100% efficiency always applies — real-world battery performance is usually somewhat lower.
- Using peak or burst current instead of the actual average sustained current draw.
Best practices
- Use a realistic efficiency factor (often 70-90%) rather than assuming ideal 100% performance, for a more accurate real-world estimate.
- For devices with variable current draw, use the average current over a typical usage cycle, not the peak.
Tips
- If your device's current draw varies significantly (e.g. active vs. sleep mode), calculate a weighted average current first for a more accurate estimate.