You can recondition cordless drill batteries that are nickel cadmium (NiCad) or nickel metal hydride (NiMH). These batteries wear down and eventually die out. You can correct this process and make your cordless drill batteries work like new again.
Remove the dead battery pack from the cordless drill.
Using the volt meter, determine which leads on your battery case are positive and negative. Mark the positive lead, so that it is easier to reassemble your battery case after the reconditioning process.
Unscrew the cordless drill battery case to open and reveal the battery cells to recondition. Take note of the inside spring so you don't lose it. This piece tends to snap out or pop away when the case is opened. Carefully lift off the top of the battery case.
Place the small screws and the spring into a small container to make them easier to find during reassembly.
Pull out the cells from the bottom casing. They should come out as one piece that is banded or shrink-wrapped together.
Mark the top of the silver cardboard insulator at the point where the wires go from the terminal into the battery pack. Again, this will make it easier to reassemble.
Remove the terminal piece with needle nose pliers. Don't let the wires cross or touch during this removal. There is a risk of electrical shock or an explosion if you let the terminal wires cross. Set this piece aside with the screws and spring.
Insulate the exposed metal band with electrical tape. This metal piece will be hot during the reconditioning process. Wrapping it in tape will protect you from injury.
Lift off the silver cardboard insulation piece that covers the rechargeable battery cells. Place this piece aside.
Cut the shrink wrap from the top of the batteries, just enough to expose the top and bottom of the battery leads.
Set the volt meter to 2 volts and test each individual rechargeable battery cell. Mark all batteries with a volt meter reading of 0 or negative. This will denote which batteries within the pack need to be reconditioned.
Prepare your external 12-volt power source to zap the batteries you have marked to recondition. Put on gear to protect your hands, eyes and skin during this potentially hazardous process.
Locate the positive and negative ends of the first battery to be reconditioned.
Hold the black alligator clamp, powered from your 12-volt source, against the negative end of the battery and the red clamp against the positive end for a maximum of two seconds.
Remove the clamps and test the battery to see whether it took the charge. If it reads more than 1 volt on the volt meter, move on and recondition the next cell. If the cell does not read more than 1 volt, zap it again. The cell can be zapped up to 10 times.
Continue the process until all cells within the battery pack have been reconditioned.
Reassemble the battery pack.
Place the reassembled battery pack onto the drill battery charger overnight. The next day your drill should work like new.
The cells within the cordless drill pack are wired together. They most often resemble C-size battery cells, with both a positive and a negative side of each battery. There is no need to separate these connections during the zapping process.