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How to Fix an 18V cordless drill Battery

Instead of scrapping it, fix your 18-volt drill battery pack. New battery packs are a costly investment, particularly for heavy users of cordless drills. Fixing your 18-v drill battery pack is similar to jump-starting a dead battery on your car. This method works for nickel cadmium and nickel hydride battery packs.

Instructions:

Determine the positive and negative leads on your battery case using the volt meter. To make it easier to reassemble your battery drill pack, mark the positive lead on your case.
Open the battery case using a small screwdriver.
Catch the small inside spring as you open the case. It tends to pop up when the case is opened.
Save these easily lost pieces by placing the screws and spring in a small container.
Pull out the internal battery pack.
Note the point at which the wires from the top terminal lead go through the silver cardboard insulation piece. Mark this point so it is easier to reassemble. For photo, see Reference 1.
Lift off the black terminal piece with a pair of needle nose pliers. Do not let the wires cross or touch during removal.
Note the exposed metal tab on the remaining battery pack. It is important to insulate this piece with tape as it will be “hot” during the jump-start process.
Remove the silver cardboard insulation piece and set aside.
Expose the tops and bottoms of the battery cells by cutting off enough shrink wrap to expose them.
Determine which battery cells will need jump-starting. It is likely that only a few of the cells are bad. Working on each individual cell, set the volt meter to 2. Any batteries with a reading of negative will need to be reconditioned.
Mark each battery that needs to be reconditioned with a black marker. Once all batteries have been tested, begin the reconditioning process.
Determine the polarity of the battery cells. The flat end is negative and the raised end is positive.
Place the black alligator clamp from the 12 volt batter charger on the negative end of the battery.
Use the red clamp to tap the positive, or raised end of the cell two or three times. Then hold the red clamp down for six seconds.
Remove all clamps and retest that battery cell with the volt meter. If it reads 1 volt, it has been successful. If it reads less than 1 volt, then repeat the process on that battery cell. This process can be repeated up to 10 times.
Continue the reconditioning process on each battery cell that you marked for reconditioning.
Once completed, reassemble the battery pack.
Place the reassembled 18v battery pack back onto the drill and set on the charger to fully recharge batteries.