🔋 Battery Capacity Calculator
Estimate how long a battery will last and how much energy it stores from its capacity, voltage, and load current.
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How battery runtime is estimated
A battery’s capacity, measured in milliamp-hours (mAh), tells you how much current it can theoretically deliver over one hour. Dividing capacity by the actual current draw of your device gives an estimate of how long the battery will last, and applying a system efficiency factor accounts for real-world losses in voltage regulation and heat.
Formulas used: Runtime (hours) = (Capacity ÷ Load Current) × (Efficiency ÷ 100), and Stored Energy (Wh) = (Capacity ÷ 1000) × Voltage.
- Efficiency accounts for voltage converters, self-discharge, and non-ideal discharge curves; 80-90% is a reasonable general estimate for most electronics.
- Watt-hours (Wh) let you compare batteries of different voltages on equal footing.
This tool gives estimates for general planning and educational purposes; actual battery runtime varies with temperature, age, and discharge rate.
Last reviewed August 2026