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.