What is it?
The Battery Life Calculator estimates how many hours a battery can run a device. It also shows how much energy the battery holds and how much power the device uses.
Who is it for?
Electronics hobbyists, people buying power banks, and engineers estimating device run time.
How to use it
Enter the Battery capacity (mAh or Ah), Battery voltage, what the Device draws (mA or A), and the Usable share of the battery. The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
Why “usable share”?
Life = capacity ÷ current × usable share. For a lead-acid battery use about 50%, for lithium 80–90%; batteries rarely give all their rated capacity. Cold weather, old age and high current reduce it further.
Examples
- A 10,000 mAh power bank charging a phone: the bank’s cells are 3.7 V but phones charge at 5 V with losses, so you get about 60–70% of the rated mAh into the phone.
- A 2,000 mAh battery powering a 100 mA device: about 20 hours at 100%, about 16 hours at 80% usable.
Different voltages
When the battery and device voltages differ, compare energy (Wh) instead of mAh: Wh = Ah × V. For home inverter batteries, use the Inverter and Battery Calculator.
Errors and how to fix them
- “Enter the current the device draws (more than 0)”
Open the tool: Battery Life Calculator
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.