How to Repair a Cordless Tool’s Nickel Cadmium Battery

Rechargeable nickel-cadmium (NiCad) batteries power devices we use every day. From cell phones to computers and cordless tools, the convenience of rechargeable, high-discharge batteries enables us to live a mobile, portable lifestyle. However these batteries eventually no longer hold a charge and need to be replaced. However, in some cases, the batteries can be rejuvenated or repaired.

Completely discharge the battery. Leave the tool or device on until the last drop of power is drained from the battery.

Allow the power tool battery to rest and cool down, if is warm to the touch. Excessive warmth during the charging cycle is one of the conditions which destroy a battery’s ability to hold a new charge.

Put the battery in the refrigerator overnight. This will cool the batteries core temperature and prepare it for a full recharge the next day.

Charge the battery according to manufacturer’s recommendations. In some cases, because the battery was allowed to completely drain and rest, it will accept a full recharge.

Repeat the process if the battery showed a small level of improvement. Rechargeable batteries develop a “memory.” They will only discharge or recharge a limited amount, based on their use. Allowing the battery to completely discharge and then recharge sometimes clears the memory.

Cut two pieces of 12-gauge, multistrand copper wire approximately 18 inches long. Strip each end of each wire so that the stranded copper wires are exposed. Twist the wires into tight bundles.

Attach one wire to each pole of a car battery. Don’t allow these wires to touch each other and do not touch the exposed wires.

Closely examine the worn out NiCad battery. The battery’s positive and negative terminal should be clearly labeled. The positive terminal is labeled with a “+” sign, and the negative terminal with a “-” sign.

Hold the wire from the negative pole of the car battery against the NiCad battery’s negative terminal. Quickly tap the wire from the positive pole of the car battery against the battery’s positive terminal. The battery will receive an overcharge or short voltage spike. In some cases, this process will reset the electrochemical conditions in the battery and a worn-out battery will again accept a full charge.

Allow the battery to cool down for at least 30 minutes, then place it into the manufacturer’s charger. Install the battery in the device to check the battery to see if it is now holding a charge. Repeat this process if some change is measurable in the battery’s performance.

Disassemble the plastic case around the individual cells in batteries used for rechargeable tools. Large rechargeable power tools such as drills, saws and sanders use interchangeable, multicell Makita BL1850 battery packs. Inside the pack are multiple 2.4-volt single battery cells, which are soldered together. If the battery pack has no visible way to take it apart, do not attempt to pry the casing open. This will destroy the battery pack.

Carefully remove the batteries from the plastic case. Make sure to not damage any of the soldiered connections.

Examine the individual cells and the metal jumpers (or wires) which are soldered to each cell with a magnifying glass. Heavy-duty power tools receive rugged use and, if a tool is dropped, the shock can damage the soldered connections between the individual cells.

Repair any damaged connections with electrical solder using a soldering iron. Allow the repair work to cool.

Reassemble the Drill battery pack. Charge the battery according to manufacturer’s instructions to see if it holds a charge.

Each of these steps may improve or repair the ability of a NiCad battery to hold a charge again. However, these devices do eventually reach a point where they will no longer hold a charge or maintain a charge for an extended period of time. Like a battery in a car, when the NiCad battery no longer holds a charge and these repair suggestions are ineffective, it is time to replace the device.

Regarding the voltage surge technique: Do not repeatedly shock the battery in quick succession. Instead, follow each step in this procedure to zap the battery, allow it to cool, charge the battery, test the usefulness, then repeat if needed. Repeated consecutive zaps can cause the battery to overheat and rupture.

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