Battery Runtime Calculator
Enter your battery size and what the tool draws, and get a realistic runtime — not the number on the box.
14 minestimated runtime
- Pack energy
- 90 Wh
- Usable energy
- 72 Wh
- Assumed draw
- 300 W
- Efficiency factor
- 80%
How this works: a battery’s energy is volts × amp-hours, so an 18V 5.0Ah pack holds about 90 Wh. You never get all of it — the pack cuts off early to protect the cells, and the motor and controller lose some to heat. That’s the efficiency factor above. Runtime is usable energy ÷ power draw.
Treat the result as a realistic estimate, not a guarantee. Actual runtime moves with temperature, battery age, blade or bit sharpness, and how hard the material fights back. A pack that’s a few years old can be well down on its rated capacity.