Battery Life Calculator
This battery life calculator finds how long a battery lasts from its capacity, the load current, and an efficiency factor. Enter them and the battery life calculator returns the runtime in hours and minutes plus the usable capacity. As a battery run time calculator it works for phones, drones, IoT sensors, and any load that draws a steady current.
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The Battery Life Calculator is part of our Electronics collection. Browse more electronics to size, convert, and check your work alongside this tool.
What the battery life calculator shows
A battery holds a fixed charge, and the battery life calculator works out how long that charge lasts at a given draw. It divides the capacity by the load current, then trims the result by an efficiency factor for the energy lost to heat and conversion. Whether you call it a battery duration calculator, a battery longevity calculator, or a battery usage calculator, it answers the same question: how many hours before the battery runs flat.
The battery life formula
The battery life formula divides capacity by load current, then applies the efficiency factor:
Capacity and load are in the same units, mAh and mA, so they divide to hours. The efficiency factor accounts for real losses, so a battery consumption calculator does not overstate the runtime. Leaving efficiency at 1 gives the ideal figure; 0.85 is a realistic default for most devices.
Battery run time calculator example
A 3000 mAh battery driving a 200 mA load at 0.85 efficiency. The battery run time calculator gives:
So the battery lasts about 12.75 hours, or 765 minutes, with 2550 mAh usable. Change the load and the battery life calculator updates the runtime at once.
How to use the battery life calculator
Enter the battery capacity in mAh, the load current in mA, and an efficiency factor between 0 and 1, then the battery life calculator returns the runtime in hours and minutes. Read the capacity off the cell and estimate the load from the device draw. An efficiency near 0.85 suits most electronics, since no battery delivers its full rated charge under a real load.
Reading the battery duration calculator result
The runtime is how long the battery holds up at that steady draw. Real devices pulse between sleep and active current, so use an average load for a fair figure. A heavier load shortens the runtime in direct proportion, so halving the current roughly doubles the hours. The usable capacity shows what the efficiency factor leaves after losses. Treat the battery duration calculator result as a planning estimate, since temperature and battery age also cut into real runtime.
When to use the battery usage calculator
- Planning runtime for a project with the battery usage calculator
- Sizing a cell with the battery run time calculator
- Comparing devices with a battery consumption calculator
- Estimating how long a power bank drives a load
Common battery life calculator mistakes
- Using peak current. Feed the battery life calculator the average draw, or the runtime comes out too short.
- Ignoring efficiency. Leaving efficiency at 1 overstates runtime; 0.85 is a safer default.
- Mixing units. Keep capacity in mAh and load in mA so they divide cleanly to hours.
Tips for longer runtime
- Lower the average current with sleep modes to stretch runtime most.
- Use an efficiency near 0.85 for a realistic estimate.
- Allow for cold weather and aging, which both cut usable capacity.
The battery life formula and efficiency
The battery life formula looks simple, capacity over current, but the efficiency factor is where estimates go right or wrong. A cell rated at 3000 mAh rarely delivers all 3000 under load: some charge is lost to internal resistance as heat, and a boost or buck converter between the battery and the load adds its own losses. An efficiency of 0.85 means you plan on 85 percent of the rated charge reaching the load, which is why the battery life calculator trims the ideal runtime. Push a high current and the efficiency drops further, since losses rise with the square of the current, so a battery drain calculator that ignores this overstates runtime for power hungry devices. When you know the load draws a fixed current, the formula is accurate; when it pulses, feed it the average.
Battery longevity calculator and consumption
A battery longevity calculator is most useful when you compare designs rather than chase a single number. Because runtime scales inversely with current, cutting the average draw is the strongest lever: a sensor that sleeps most of the time and wakes briefly can run for months on the same cell that lasts hours in an always on device. That is why a battery consumption calculator pairs well with duty cycle planning, where you weight the sleep current and the active current by the time spent in each. Capacity helps too, but doubling capacity only doubles runtime, while halving the average current does the same for less weight. Use the power calculator to see the power each mode draws, then average the current for a realistic longevity figure.
Battery life calculator runtime chart
Runtime from the battery life calculator at 0.85 efficiency for common capacity and load pairs:
| Capacity | Load | Runtime |
|---|---|---|
| 2000 mAh | 100 mA | 17.0 hours |
| 3000 mAh | 200 mA | 12.75 hours |
| 3000 mAh | 500 mA | 5.1 hours |
| 5000 mAh | 200 mA | 21.25 hours |
Battery Life Calculator FAQ
What is the battery life formula?
The battery life formula is hours = (capacity divided by load current) times efficiency. The battery life calculator applies it, with capacity and load in mAh and mA.
Why include an efficiency factor?
A battery never delivers its full rated charge under a real load, since some energy is lost to heat and conversion. An efficiency near 0.85 keeps the battery consumption calculator realistic.
What load current should I use?
Use the average current the device draws, not the peak. Most devices pulse between sleep and active, so an average gives the battery run time calculator a fair figure.
Does temperature change battery life?
Yes. Cold and heat both cut usable capacity, and cells lose capacity as they age, so treat the battery duration calculator result as a planning estimate.