Although your cordless drill battery no longer holds a charge, there may still be some life left in it. An 18-volt cordless drill battery pack can be revived using a process similar to jump-starting a dead car battery. This process should only be performed on Nickel Cadmium (Nicad) and Nickel Metal Hydride (NiMH) battery packs.
Test your dead cordless drill battery pack using the volt meter to verify which lead in your battery case is negative and which is positive. Clearly mark which point is positive and which is negative on the battery case to ease the difficulty of later reassembly.
Use a small screwdriver to open the drill battery case. Watch out for the spring inside of the case because it tends to pop out and can easily get lost. Save the screws and spring by placing them in a small container.
Lift off the top of the cordless drill battery case to expose the inner battery cells. These cells will look like a grouping of C batteries that are joined together in one link.
Remove the battery cells from within the bottom of the drill casing. These will come out as one unit as they are banded or shrink-wrapped together.
Locate the point where the wires run from the terminal piece down through the silver cardboard insulator. The terminal piece should be black or silver and located on top of the silver cardboard insulation, with the batteries beneath the cardboard. Mark the silver cardboard insulator at the exact point where the wires pass through the silver cardboard insulation. Again, this will make it easier to reassemble.
Release the terminal piece from the silver cardboard insulation using needle-nose pliers. Take care not to let the terminal wires touch or cross during this process as you are at risk for electrical shock or even an explosion. Set the terminal piece aside along with the battery case screws and spring.
Note the exposed metal band on the side of the battery pack. It is important to insulate this band with electrical tape prior to starting the process. This metal piece will be hot during the reconditioning process and insulating it with electrical tape will protect you from injury.
Remove the silver insulation piece that covers the top of the rechargeable battery cells. Place this piece aside to be used in reassembly.
Remove any plastic covering from the top section of the battery pack so you can access both the top and bottom of the rechargeable battery leads.
Turn on the volt meter and set it to a reading of two volts. Check each individual battery cell and mark each battery cell that gives a reading of zero or negative. These will be the cells that will need to be reconditioned.
Prepare your external 12-volt power source, including alligator clamps, for the reconditioning process. Protect your hands, eyes and skin with protective clothing and safety gear during this potentially hazardous process.
Locate the positive and negative ends of the first battery to be reconditioned. The positive end will be raised and the negative ends will be flat.
From the 12-volt source, hold the black alligator clamp to the negative end of the battery and the red alligator clamp to the positive end for two seconds.
Release the clamps and use a battery test to see if the battery has been fully charged. Repeat the process if necessary. The rechargeable battery cell can be zapped up to 10 times. Continue reconditioning the remaining batteries.
Reassemble the battery pack.
There is no need to separate each individual rechargeable battery cell from the pack during the zapping process.
Be sure not to cross wires to prevent a possible explosion. If you are uncomfortable working with this equipment, do not attempt this process. Other hazards include leaking or spraying battery acid and a potential for a fire if the battery is overcharged. Individuals attempting to repair their 18V drill battery do so at the risk of injury to themselves, others, property and tools.