Disassemble the Dewalt Battery Pack

• Locate the small screws along the outer edge of the Dewalt battery pack casing. Use a screwdriver to remove these screws. Set them aside for later reassembly. Prior to opening the case, note that many battery packs contain an internal spring that tends to pop out when the case is open. When opening the case, take care not to lose this spring. Remove the cells from within the case. Take care to note how these batteries sit in the Dewalt battery case, particularly in terms of polarity, for later reassembly.
  
  

Replace "bad" cells.

• Determine which cells have gone bad. Use a battery tester to test each and every cell within the chain. Mark each cell that is dead or not fully charged for replacement. De-solder the first "bad" battery cell to be replaced. Take a new rechargeable battery and re-solder it into the chain. Make sure the new battery is soldered in the exact same polarity position as the original battery. When replacing bad cells, make sure that you are substituting rechargeable batteries of the exact same size and type. For example, size A nickel metal hydride batteries should only be replaced with sized A nickel metal hydride batteries - do not mix types of batteries within the chain. Continue to perform this process on all of the "bad" cells.
  
  

Charge the Dewalt Battery Pack

• Return the battery chain to the Dewalt battery case. Re-screw the casing closed. Place the Dewalt battery pack on the charger overnight.