An 18-volt Dewalt battery is made up of 12 size C rechargeable battery cells linked in a series. Each of these cells is linked together in a chain of batteries to provide a total of 18 volts of power. The 18V Dewalt battery can die if even one out of the 12 rechargeable battery cells dies. Refurbish your 18V Dewalt battery by making repairs to the dead C battery cells within the battery pack.
Open the Dewalt battery pack with a screwdriver, placing the screws aside for later reassembly. Older Dewalt models may have sealed battery cases. In this situation, use the chisel tip on the soldering iron to cut open the top of the battery pack.
Remove the batteries from the casing, keeping them in the same formation as they were in the Dewalt case.
Copy the pattern of how the battery cells are linked together. This will allow for much easier reassembly. Note which cells are linked positively and negatively together.
Use the battery tester to determine which cells within the battery pack have gone bad. A reading of 1.5V means the cell is still good; a 0.8 reading or less means the cell is bad.
Mark each malfunctioning cell for refurbishing.
Remove the defective battery cells by desoldering the leads that link the defective cells into the battery chain.
Using the 12-volt power source, hold the black alligator clamp to the negative end of the battery and the red alligator clamp to the positive end of the battery for no longer than 3 seconds. Remove the clamps immediately.
Recheck the power level on that cell to determine if it reaches 1.5 volts. If not, repeat the charging process.
Repeat this process on each of the “bad” size C rechargeable batteries in the chain.
Once they have all been refurbished, begin resoldering the battery cells back into the chain.
Place the batteries back into the Dewalt battery case. Screw the case back together. If the case had to be cut open, glue or duct tape the case back together.
Place the refurbished battery case back on the charger overnight to charge the entire unit.