Free phone battery life calculator. Enter battery capacity and average power draw to estimate runtime in hours and minutes on one charge.
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Divide battery capacity in milliamp hours by average power draw in milliamps to get runtime in hours, then multiply by 60 for minutes. The result is an ideal figure: real runtime varies because screen brightness, signal strength and apps change power draw minute by minute, and because usable capacity is usually 80 to 85 percent of the rated figure. For a realistic estimate, multiply the result by 0.85.
Battery capacity and power draw are a simple division. A 4000 mAh battery drawn at 350 mA lasts about 11.4 hours, or 686 minutes. The hard part is not the maths but the draw figure, since gaming draws far more than reading, and weak mobile signal can raise draw sharply.
Milliamp hours measure charge capacity: a 1000 mAh battery can supply 1000 mA for one hour, or 100 mA for ten hours. A 5000mAh phone battery at 250 mA of average draw lasts about 20 hours in ideal maths, and a full day of mixed use in practice, with 6 to 8 hours of screen on time.
Typical draws from competitor tables help you pick a realistic input: a smartphone on standby draws about 3 to 15 mA, active screen use draws about 150 to 400 mA, a tablet draws about 100 to 500 mA, a smartwatch about 15 to 80 mA, and earbuds about 20 to 60 mA per bud. Always use average draw, not peak draw.
Enter your phone battery capacity from its specifications and an average draw estimate, or try 250 mA for light use, 350 mA for mixed use and 600 mA for heavy use. Compare results to see how lower brightness or fewer background apps could extend your day.
Rated capacity is measured in a lab, so usable capacity is lower in real life. At 80 percent efficiency, a 3000 mAh battery delivers 2400 mAh, which lasts 16 hours at 150 mA instead of 20 hours. Cold, high currents and aged cells all push usable capacity down further.
Watt hours measure energy, and the conversion is Wh equals mAh times volts divided by 1000. A 5000mAh battery at 3.7 volts holds 18.5 Wh, which is the fair way to compare batteries at different voltages, since mAh alone ignores voltage.
Screen on time is the biggest drain, followed by gaming, video, GPS and weak signal. Cold weather also cuts delivered capacity, and battery age degradation means an older phone holds less charge than when new, so the same draw gives shorter runtime.
Lower screen brightness, use auto brightness, turn off unused radios, restrict background apps and use battery saver mode. Keeping the phone cool and avoiding full discharges also slows degradation, so the same battery keeps more of its capacity over time.
Milliamp hours measure charge capacity. A larger mAh number usually means a longer lasting battery, but screen size, processor efficiency and software also decide real battery life.
It depends on average draw. A 5000mAh phone usually lasts about a full day of mixed use, with 6 to 8 hours of screen on time, while light use can stretch it to two days.
At 250 mA average draw, ideal maths gives 20 hours. In real use, with 80 to 85 percent usable capacity, expect roughly 16 to 17 hours of continuous mixed use.
Screen time, gaming, video, weak signal, GPS and background apps all raise power draw. On a heavy day your average draw may double, which roughly halves the runtime this calculator estimates.
Cold slows the chemical reactions inside the cell and raises internal resistance, so less capacity is delivered before the phone shuts down. Warming the phone back up usually restores most of the apparent loss.
Yes. Lithium batteries lose capacity with age and charge cycles, roughly 20 percent over 500 cycles for many phones, so an older battery gives shorter runtime at the same draw.
Check the battery usage screen in settings for screen on time and app share, or use a USB power meter for a direct reading. Use an average across a normal day, not a peak gaming figure.
Yes, the same maths applies, but watch the voltage: a power bank rated at 3.7 volts delivers less energy at 5 volt USB output, so convert to Wh first for a fair estimate.
Screen on time is the total time the display is lit and in use. It is the single most useful measure of a phone day, because the screen is usually the largest power draw.