Estimate how long a battery will power your device. Enter the battery capacity and the device’s current draw to get an instant runtime estimate — ideal for DIY electronics, RC models and off-grid planning.
This is a theoretical estimate. Real runtime is affected by temperature, battery age and how the current draw varies over time.
How to Use
- Enter the battery capacity in milliamp-hours (mAh) — printed on most batteries.
- Enter your device’s current draw in milliamps (mA) — check the manual or measure it.
- Read the estimated runtime instantly, shown in hours, minutes and days.
Key Features
- Instant runtime estimate from capacity and current draw.
- Results in hours and minutes, decimal hours and days.
- Live recalculation as you type.
- Works for any battery chemistry or device type.
- Private — everything runs in your browser.
FAQs
What does mAh mean?
Milliamp-hours measure a battery’s charge capacity. A 3000 mAh battery can theoretically supply 3000 mA for one hour, 1500 mA for two hours, and so on.
How accurate is the estimate?
It is a good first approximation. Real-world runtime is usually a little lower because of conversion losses, temperature, battery age and uneven current draw.
Can I use it for a power bank?
Yes. Enter the power bank’s rated capacity and your device’s charging current to estimate how long it can keep charging. Knock off around 15–30% for conversion losses.
Does a bigger battery always last longer?
All else being equal, yes — runtime scales directly with capacity. But a more efficient device on a smaller battery can still outlast a power-hungry one on a bigger battery.
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