Battery Runtime Calculator
Estimated runtime from battery capacity and load current.
Enter your values
Enter the battery capacity in Ah.
Enter the load current in A.
Enter the usable efficiency in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Estimated runtime
- 5.67 hours
- Estimated runtime
- 340 minutes
- Usable capacity
- 8.5 Ah
Quick answer
Runtime (hours) = battery capacity (Ah) x efficiency / load current (A).
t = (Ah x eff) / I
At a glance
| What it does | Estimated runtime from battery capacity and load current. |
|---|---|
| Category | Engineering |
| Inputs needed | Battery capacity, Load current, Usable efficiency |
| Main output | Estimated runtime |
| Formula | t = (Ah x eff) / I |
| Cost | Free — no sign-up, no download |
How to use the Battery Runtime Calculator
- 1Enter the battery's rated amp-hour capacity.
- 2Enter the average current the device draws.
- 3Apply an efficiency factor to account for voltage sag and conversion losses.
Inputs explained
- Battery capacity(Ah)
- Enter the battery capacity in Ah.
- Load current(A)
- Enter the load current in A.
- Usable efficiency(%)
- Enter the usable efficiency in %.
Worked example
Using the values the calculator loads with:
Inputs
- Battery capacity10 Ah
- Load current1.5 A
- Usable efficiency85 %
Results
- Estimated runtime5.67 hours
- Estimated runtime340 minutes
- Usable capacity8.5 Ah
Frequently asked questions
Why not use 100% efficiency?
Real batteries lose usable capacity to internal resistance, temperature and discharge rate effects (Peukert's law).
How do I find load current?
Check the device's power rating and divide by its operating voltage, or measure directly with a multimeter.
What do I need to enter into the Battery Runtime Calculator?
Just 3 values: battery capacity, load current, usable efficiency. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Battery Runtime Calculator work out the answer?
Runtime (hours) = battery capacity (Ah) x efficiency / load current (A). It applies the formula t = (Ah x eff) / I and shows the working so you can check each step by hand.
Is the Battery Runtime Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.