Battery life calculator
This battery life calculator estimates run time from capacity and load. Example: a 5,000 mAh battery drawing 250 mA lasts 16 hours at 80% usable capacity.
Example: Values in: mAh and mA (current) · Battery capacity (mAh) 5,000 · Current draw (mA) 250 · Usable share (%) 80 → Battery life: Battery life ≈ 16 h. Source: Wikipedia – Ampere-hour. Updated: .
How it is calculated
Battery life is the usable capacity divided by the load. That holds for a phone, power bank, camera, drone or meter alike, as long as you know the average consumption.
Formulas
With current: run time in hours = capacity (mAh) × usable share ÷ current draw (mA). With power: run time = capacity (Wh) × usable share ÷ power (W). The usable share is a flat estimate, because voltage converters, ageing and cold use up part of the rated capacity.
Examples
5,000 mAh × 0.8 = 4,000 mAh usable; at 250 mA that is 4,000 ÷ 250 = 16 hours. With power: 50 Wh × 0.8 = 40 Wh; at 10 W that gives 4 hours. Watt-hours come from mAh × voltage ÷ 1000.
- Peak loads, such as transmitting or brightening the display, shorten the run time below the average.
- As a battery ages, its real capacity drops.
Frequently asked questions
How do you calculate battery life?
Usable capacity divided by the load. With 4,000 mAh usable and 250 mA that is 16 hours.
How do I convert mAh to Wh?
Wh = mAh × nominal voltage in volts ÷ 1000. At 3.7 V, 5000 mAh is about 18.5 Wh. The mAh to Wh converter does this for you.
Why is real-world run time often shorter?
Because consumption fluctuates, converter losses and ageing cost capacity, and cold reduces usable energy. That is why the usable share includes a flat allowance.
Sources and legal basis
- Wikipedia – Ampere-hour
- Wikipedia – Watt-hour
- Linden, Reddy: Handbook of Batteries – Battery characteristics (capacity, discharge)
As of: · Editorial policy
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