Nickel cadmium (NiCad) battery packs contain individual cells wired in series. The number of cells in the pack depends on the output voltage. NiCad cells produce 1.2 volts and 700 milliamp hours so a battery pack producing 12 volts contains 10 cells. NiCad battery packs can only be charged a certain numbers of times before you find they no longer hold a charge. The number of times you can charge a NiCad battery pack depends on how you charge and discharge the battery. If you are reasonably proficient at do-it-yourself tasks then rebuilding a NiCad battery pack is less expensive than purchasing a new one.
Check how the battery cover on the NiCad pack is held in place. Many have small Phillips screws, so you can easily remove the cover. However, some NiCad battery packs are sealed units. If you find it is a sealed unit its best not to try and force the cover open. You will damage it making it difficult to replace. This could be dangerous. It's sensible to resign yourself to buying a new one, but this time ensure you get one that has a screw-fitting battery cover.
Check the label on the NiCad battery pack to determine the output voltage. Divide the output voltage by 1.2 to calculate the number of cells you need to buy. Replacement cells can be purchased at most electrical or hobby stores.
Remove the screws from the NiCad battery pack using a small Phillips screwdriver. Carefully lift the battery cover from the main unit. In most cases the cover can be completely removed, but some have wires that connect between the battery cover and the cells so you can only remove it enough to get access to the cells.
Locate several small screws on the inside of the NiCad battery compartment. These hold the cells in place. Remove the screws using a screwdriver and then lift the complete cell pack from the battery compartment. You can clearly see all the cells.
Check how the cells are held in place. Most have metal plates that connect between the battery terminals and are soldered in place. If you are fortunate, the cells clip into place making it easy to remove them. Follow the steps in Section 2, if the cells clip in place, or follow the steps in section 3, if they are soldered.
Use a small screwdriver and gently insert it down the side of the where a cell terminal connects to the battery pack. Carefully lever the cell upward until it is released from the cell compartment. Remove the cell using your fingers and place it to one side.
Repeat the process until all the cells are removed. Place all the old cells into a clear plastic bag as you will need to dispose of them in a battery recycling unit. NiCad batteries must not be put in your regular trash.
Put your new NiCad cells into the battery compartment. Ensure the terminals are correctly aligned to the connectors. The cells and the connectors are labelled "+" and "-" so make sure you connect "+" to "+" and "-" to "-." Push the cell into place using your fingers. You hear it click when it's seated correctly. Repeat until all the cells are replace.
Insert the battery cells into the battery compartment and replace the screws so the cells are held in place. Replace the battery cover and tighten the screws using the screwdriver.
Put you Rebuilt NiCad battery on charge for an hour. This ensures that all the cells are fully charged.
Heat a soldering iron. Have a small pair of pliers nearby. Place the hot soldering iron on top of one of the metal plates immediately above a soldered connection. You can see the soldered connections by looking down the side between the metal plate and the cells. Put your pliers on the end of the metal plate and as the solder melts remove the soldering iron and slightly lift the plate from the cell terminal. Put the end of the soldering iron on another soldered part and repeat the process until the plate is removed. Repeat until all the metal plates are removed. Turn off the soldering iron.
Remove the cells from the battery compartment. Place the cells into clear plastic bag as you need to put them in a recycling unit. Don't put them in your regular trash. Put the new cells into the battery compartment. Ensure that the "+" and "-" markings on the cell terminals connect to the respective markings on the battery connectors.
Heat a soldering iron. Put the end of the soldering iron on a cell terminal. Introduce a little solder and let it melt. Remove the soldering iron and solder as soon as it melts. Repeat the process on every cell terminal.
Place the metal plate onto the cells using the pliers. Put the end of the soldering iron on the metal plate directly over a cell terminal and let the solder melt. Remove the soldering iron and repeat the process on the other cells so the plate is securely soldered to the cells. Turn off the soldering iron.
Put the cell pack into the main battery compartment. Replace the screws using a screwdriver so the cells are held in position. Replace the battery cover and screw the screws into the holes and tighten them using the screwdriver. Put the rebuilt NiCad battery pack on to charge for an hour to ensure all the cells are fully charged.