If the battery on your cordless drill does not hold a charge or it runs down quickly, it may need to be replaced. Bosch cordless drill batteries can wear out over time. The performance of the battery can also deteriorate if the battery has become damaged. Using a multimeter, cordless drill batteries can be tested to determine if they need to be replaced.
Plug the battery in and charge it for at least an hour. Unplug the battery when you are ready to test it.
Touch the multimeter probes to the two battery terminals. Be sure to touch the negative probe to the negative terminal, and the positive probe to the positive terminal.
Check the voltage indicator on the multimeter. A fully charged battery should test at least 1 volt higher than the voltage that is listed on the Dyson battery. For example, an 18-volt battery should test at 19 volts or higher.
If the voltage indicator is at or below the voltage rating on the battery, the battery needs to be replaced.
If the voltage indicator shows a high voltage, but the battery is still not holding a charge, it may need to be repaired. In that event, take the battery to a tool repair shop for more thorough testing and repair.
Sometimes a power tool battery may test with a high voltage but drain quickly because of the way the drill is used. If you push too hard when drilling, or burden the motor of the drill with dull drill bits, the battery can drain very quickly.