Cordless Power Tools – Battery Run Time Explained

The below illustration shows the relationship between Volts, Ampere-hours, and Watts using a car to better understand the concept of rechargeable batteries. It is often asked how long the batteries will last; this is a tricky question as it all depends on what battery is used and how it is used. In the example of a car, the Ah rating of the battery is the size of the fuel tank. The larger the fuel tank or Ah rating the longer the battery will last. Also, the way you drive will also affect fuel consumption, the faster you go the more power (watts) you use. The more power that you use the more fuel (Ah) is used.

Volts (V):

The voltage data (V) shows the amount of voltage of the rechargeable battery. In comparison to a car, this would be the size of the engine, in other words, the displacement and therefore the power of the engine.

Ampere-hours (Ah):

The ampere-hours data (Ah) shows the operational performance which is possible with the device being operated. For a car this would correspond to the petrol tank capacity; the bigger it is, the longer you can drive with it.

Watts (W):

The watt data (W) shows the amount of power that can be supplied by the rechargeable battery. In comparison to a car, this would be the engine output or the horsepower.


  1. A cordless drill using a 1 x 4.0Ah battery will be able to screw in about 700, 6mm x 60mm screws into softwood. this could be done all at once or over a few days.
  2. A cordless blower/vacuum using 2 x 4.0Ah batteries will run for 22-65 minutes continuously. The runtime largely depends on the fan speed selected.

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