Nickel cadmium (NiCad or NiCd) battery packs are used to power many electrical devices, particularly cordless power tools. NiCad battery packs contain numerous individual cells that are wired together in a series to produce the voltage necessary to power your electrical device. Each NiCad cell produces 1.2 volts, but the milliamp hour rating (mAh) varies, depending on the type of cell. Test your NiCad battery pack to find out the voltage and mAh using a multimeter.
Check the label on the NiCad battery pack to determine the output voltage and mAh, if it is fully charged. The voltage is always a multiple of 1.2 so if the voltage is 6 volts, the pack contains six cells. The mAh will also be divisible by the same number of cells.
Select "Voltage" on your multimeter. Put the metal prongs on the end of the wires from the multimeter onto the positive and negative terminals of your NiCad battery pack. The terminals are clearly labelled "+" and "-." The prong from the red wire goes to the "+" terminal and the prong from the black wire goes to the "-" terminal.
Look at the multimeter display and read the voltage. It should read the same as the label on the NiCad battery pack, if the battery is fully charged. If the voltage reading is lower by more than about 20 per cent you need to consider recharging the battery. Voltage readings stay fairly stable throughout discharge and then start to drop quite suddenly when the batteries are nearly fully discharged.
Keep the prongs on the NiCad battery pack and change the multimeter settings to measure amperes. Read the multimeter display. It should read the same as your NiCad battery pack label, if your battery is fully charged. You can tell how long your battery can last by comparing the reading on the multimeter to the mAh rating on the device the NiCad battery pack powers. For example, if the reading is 1,200 mAh and the electrical device has a rating of 300 mAh, your battery will power your device for four hours. However, if the reading is 100 mAh and your device has a rating of 300 mAh the battery will only power the device for about 20 minutes.