Milwaukee cordless power tools use various types of rechargeable batteries to power their devices, depending on the voltage requirements of the power tool. Rechargeable batteries containing nickel cadmium (NiCad) and nickel metal hydride (NiMH) cells have been used until fairly recently, but lithium technology has meant that these battery packs are being superseded by more powerful and lighter lithium ion (Li-ion) batteries. For example, a Milwaukee 14.4 volt NiCad or NiMH battery pack has 12 cells, while a 14.4 volt Li-ion battery pack only has four cells, resulting in much smaller and lighter battery packs.
Charge your Milwaukee battery pack until it's fully charged. Test each cell in the pack to determine if any cells are bad. Leave the battery pack alone for about eight hours, as this allows time for bad cells to lose their charge.
Remove the battery pack from the Milwaukee charger. Look for small screws that hold the battery pack cover in place. They are evenly spaced around the rim of the cover, but you may find a few hidden under the battery pack label. Remove all screws using a suitably-sized screwdriver.
Lift the cover from the base unit. You may need to carefully insert a small flat-head screwdriver under the rim to help loosen it. The cover doesn't completely come off the base unit, as there are wires linking to it, so just remove it as far as you can without disturbing the wiring. You will see the battery pack cells inside the base unit. Lift the battery pack from the base unit using your hands.
Test the voltage from each cell using a voltmeter. Place the metal sensor on the red wire/prong from the voltmeter onto the positive terminal of one of the cells. Place the sensor on the end of the black wire/prong from the voltmeter onto the negative terminal of the same cell. Each cell is labeled on one end "+" for positive, and on the other end "-" for negative. The type of cells used in the battery pack is printed on the battery cover label. It says NiCad, NiMH or Li-ion. NiCad and NiMH produce 1.2 volts, if they are in good condition, while Li-ion cells produce 3.6 volts.
Note the voltage from the cell on the voltmeter. If the cells are NiCad or NiMH, and the voltmeter reading is between 1.1 and 1.2 volts, the cell is good. If the cells are Li-ion, and the voltmeter reading is between 3.4 and 3.6 volts, the Li-ion cell is good. If the reading is less than 1.1 and 3.4 volts, respectively, the cell isn't retaining its charge. Replace these batteries.Test the remaining cells using the voltmeter. Put a mark on all cells that are bad.
Remove the bad cells from the battery pack. The cells are held in place by metal strips that are soldered on the cell terminals. Heat a soldering iron to remove them.
Put the soldering iron gently on the metal strip over the position where it is soldered to the terminal. Let the heat from the soldering melt the solder and, as it melts, immediately lift the metal strip away from the battery terminal using a small pair of pliers. Repeat the process on all the metal strips holding the bad cells in place. Turn off the soldering iron.
Take one bad battery to a hardware store, to ensure you replace it with the exact same battery. Purchase as many cells as you need to replace the bad cells you removed from the battery pack.
Put the new cells in the battery pack. Heat the soldering iron. Put the metal strips in place. Insert a strip of solder between the metal strip and the cell terminal. Put the end of the soldering iron on the metal strip exactly where the cell terminal is. Wait for the solder to melt, then immediately remove the soldering iron and solder. Let the soldered connection cool completely, then repeat the process for the remaining connections. Don't allow the cell to get hot during the process, as this will damage it. Solder each cell as quickly as possible. Turn off the soldering iron when you have soldered all necessary terminals.
Replace the cell pack in the base unit once it has cooled. Replace the battery cover, and then replace and tighten the screws using a suitably-sized screwdriver.
Charge the Milwaukee battery pack for about an hour. This tops-up the charge equally in all the batteries. Remove the battery pack from the charger, and use it in your Milwaukee power tool.