About this Battery Life Calculator
Whether you are building an Arduino project, planning a camping trip with a power bank, or testing an IoT sensor, knowing your battery life is essential. This calculator uses the standard capacity formula adjusted for real-world efficiency losses.
Who this calculator is for
- Makers, electronics hobbyists, and embedded developers estimating runtime from a known battery pack.
- Field teams planning portable power banks, radios, or sensor deployments.
- Anyone checking whether a device load is realistic for a given battery size.
When to use it
- Use it to estimate runtime for a low-power microcontroller, modem, or appliance.
- Use it when comparing battery capacities before buying a power bank or pack.
- Use it as a quick planning estimate before measuring real runtime with test equipment.
How to use this calculator
- Enter the Battery Capacity (usually printed in mAh or Ah).
- Enter the Device Consumption (Load) in mA.
- The result is the estimated Runtime in hours.
Key assumptions
- Capacity and current draw should be entered in matching mAh and mA-style units.
- The estimate uses a fixed 85% efficiency factor rather than a chemistry-specific discharge curve.
- Battery runtime is undefined when the load current is zero or negative.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
The theoretical formula is `Capacity / Load`. However, batteries are never 100% efficient due to internal resistance, temperature, and voltage drop. We apply a standard 0.85 (85%) efficiency factor (Peukert's Law simplification) to provide a realistic estimate.
Time = (Capacity × 0.85) / Load
Time = (Capacity * 0.85) / Load
Inputs explained
Capacity (mAh)
Milliamp-hours. The total amount of energy stored. 1000 mAh = 1 Ah.
Consumption (mA)
The current draw of the device. Check the spec sheet or use a multimeter.
Understanding your results
The result is an estimate. High discharge rates (heavy loads) reduce effective capacity more than light loads. Extreme cold also reduces battery life.
Example scenarios
IoT Sensor
2000 mAh battery. 10 mA load. Runtime ≈ 170 hours (7 days).
LED Strip
5000 mAh battery. 500 mA load. Runtime ≈ 8.5 hours.
Key Features
- Efficiency Factor included
- Instant Estimation
- Hours & Minutes output
Tips & Best Practices
- If using a Lead-Acid battery, the effective capacity drops significantly at high loads (Peukert effect).
- For Li-Ion batteries, avoid draining to 0% to extend lifespan.
- If your battery lists Watt-hours (Wh), calculate mAh = (Wh / Voltage) * 1000.
Glossary of Terms
- mAh
- Milliamp-hour. A unit of electric charge.
- Derating
- Reducing the rated capability of a component to account for operating conditions.
- Peukert's Law
- A formula that expresses how the capacity of a lead-acid battery decreases as the rate of discharge increases.