Free Battery Runtime Calculator
Estimate how long a battery will power a load, allowing for depth of discharge and efficiency.
What is the Battery Runtime Calculator?
Estimate how long a battery will power a load, allowing for depth of discharge and efficiency.
Capacity is converted to watt-hours using voltage, then multiplied by usable capacity and efficiency percentages. Runtime is the usable watt-hours divided by the load in watts.
Quick, reliable engineering arithmetic saves time on site and in the workshop. These tools show their working so you can check the result.
How to use the Battery Runtime Calculator
Using the battery runtime calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.
Step 1
Enter your values, choosing the units you are working in.
Step 2
Read the result and the supporting numbers shown beneath it.
Step 3
Check the result against a second method or a reference table before you rely on it.
Tips for better results
Real runtime varies with temperature, battery age and discharge rate. Lead-acid batteries are usually discharged to about 50 percent, so lower the usable capacity setting for them.
Keep units consistent from start to finish.
These tools are for estimates. Safety critical designs need a qualified engineer.
Privacy and where your data goes
Everything you type into the battery runtime calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.
Frequently asked questions
How do I convert amp-hours to watt-hours?
Multiply amp-hours by battery voltage. A 100 Ah, 12 V battery stores 1,200 Wh.
What does usable capacity mean?
It is the share of the battery you allow yourself to use. Draining deeper can shorten battery life, particularly with lead-acid types.
Is the battery runtime calculator free?
Yes. It is free to use with no signup, no watermark and no usage limits.
Is my data private?
Yes. Your inputs are processed in your browser and saved only in its local storage. They are not uploaded to our servers.
Does it work on mobile?
Yes. Zapxa works on phones, tablets and desktops. Use the print button or download a PDF to keep a copy.
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