Battery Life Calculator
Estimate how long a battery will last. Enter the battery capacity in mAh, the device's current draw in mA, and an efficiency percentage, and the tool returns the runtime in hours. Free and runs in your browser.
What this calculator does
The Battery Life Calculator estimates your result instantly from the values you enter, using standard science & engineering formulas. Estimate how long a battery will last. Enter the battery capacity in mAh, the device's current draw in mA, and an efficiency percentage, and the tool returns the runtime in hours. Free and runs in your browser. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About Battery Life Calculator
The Battery Life Calculator estimates runtime from three inputs: the battery capacity in milliamp-hours, the device's current draw in milliamps, and an efficiency percentage that accounts for real-world losses.
It divides capacity by load and scales the result by the efficiency, giving an estimated runtime in hours rounded to two decimals.
Formula & Mathematical Calculation
Estimated Runtime (hours) = f(Battery Capacity (mAh), Device Load (mA), Efficiency %)
Calculated according to standard science formulas implemented in the calculator core.
Calculation Example
For a 3000 mAh battery, a 200 mA load, and 80% efficiency:
Runtime = (3000 ÷ 200) × (80 ÷ 100) = 15 × 0.8 = 12 hrs
Key Benefits
- Estimates battery runtime from capacity, load, and an efficiency factor
- Includes an efficiency percentage to reflect real-world losses rather than an ideal figure
- Shows the runtime in hours rounded to two decimals
- Free, browser-based, and needs no sign-up
How to Use this Calculator
-
Enter the battery capacity
Type the capacity in milliamp-hours into the Battery Capacity (mAh) field, for example 3000. -
Enter the device load
Type the current draw in milliamps into the Device Load (mA) field, such as 200. -
Enter the efficiency
Type an efficiency percentage between 1 and 100 into the Efficiency % field, then select Calculate.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- Battery Life Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.