tech calculator
Estimate runtime from battery capacity, average load, and voltage.
Battery-powered devices are everywhere—from phones and laptops to sensors, routers, and DIY electronics projects. When you pick a battery or power bank, you almost always want to know the same thing: how long will this actually run before it dies?
This battery life calculator turns the capacity on a battery label (in milliamp-hours) and your device’s current draw (in milliamps) into a clear runtime estimate. By adding nominal voltage, it also gives an approximate energy figure in watt-hours plus a simple percent-per-hour drain estimate. It’s ideal for IoT prototypes, power bank planning, and quick “is this big enough?” checks without building a full spreadsheet.
Capacity in milliamp-hours (mAh) is a measure of charge: in an ideal linear model, a 5,000 mAh pack could supply 5,000 mA for 1 hour, 500 mA for 10 hours, or 250 mA for 20 hours.
The calculator uses that relationship to estimate runtime with Runtime_hours ≈ Capacity_mAh ÷ Draw_mA, assuming an average current draw that stays roughly constant over the period.
Runtime_days is then derived by dividing hours by 24 so you can quickly see whether you’re talking about hours, days, or fractions of a day.
To estimate stored energy, the tool converts mAh to amp-hours (Ah) by dividing by 1,000 and multiplies by battery voltage: Battery_Wh ≈ (mAh ÷ 1,000) × Voltage. This gives watt-hours, which is helpful when comparing packs with different voltages.
Percent consumed per hour is calculated as (Draw_mA ÷ Capacity_mAh) × 100. If this value is 10%, you can intuitively think “roughly 10 hours of runtime” under ideal conditions.
The underlying model is intentionally simple and does not simulate non-linear discharge curves, converter losses, or depth-of-discharge limits, so real runtimes typically come in below the idealized numbers—especially in cold conditions or with older cells.
Let C_mAh = capacity (mAh), I_mA = draw (mA), V = voltage (V).\n\nRuntime_hours ≈ C_mAh ÷ I_mA\nRuntime_days ≈ Runtime_hours ÷ 24\nBattery_Wh ≈ (C_mAh ÷ 1,000) × V\nPercent_per_hour ≈ (I_mA ÷ C_mAh) × 100
This battery life calculator converts battery capacity in mAh and device draw in mA into estimated runtime in hours and days, plus approximate watt-hours and percent of battery used per hour.
Use it to size batteries and power banks, plan IoT and embedded deployments, or sanity-check manufacturer runtime claims. Then layer in real-world losses and aging for production designs.
This battery life calculator is a simplified planning tool based on nominal capacity, average current draw, and nominal voltage. It does not model detailed discharge curves, thermal effects, converter efficiency, or safety margins. Always validate runtimes with manufacturer specifications and real-world testing, especially for safety-critical or mission-critical designs.
