NiCad batteries, or Nickel Cadmium batteries, are one type of rechargeable battery on the market today. This is a battery that has a "memory effect," which means that it does not keep a strong charge. It gives a lesser charge residually as you continue to charge and reuse it. Zapping, or shocking, one of these batteries is fine to do, especially if it is not holding a charge very well. But if the battery is not holding a charge at all, then it needs to be discarded and replaced.
Check the voltage of the batteries with the digital multimeter.
Divide the rated battery voltage by the number of cells.
Try to revive the battery if the result is 1.0 volts per cell.
Attach the red cable of the AC adaptor to the positive end of the battery, and the black cable to the negative end of the battery.
Let sit for 1 minute.
Remove the cables from the battery ends.
Test voltage again with the digital multimeter. The equation should be performed again and the end result should be 1.2 volts per cell.