I bought two of these 19.2v lithium batteries for my Craftsman Drill on eBay and was very happy with their low weight and high power. The joy ended after only one or two recharges, as the batteries would no longer charge. The charger would show the fully charged green indicator light even though it had no charge. Worse, the company who sold them to me was no longer registered on eBay. It looked like a total loss. Out of curiosity I took one apart to see if I could figure out the problem. Nothing was obviously the problem as far as the circuit board was concerned. The thought occurred to me that the batteries might be good and could be charged with another charger. I simply removed the circuit board, verified that the batteries were connected in series and bought a universal laptop charger with multiple voltage settings. I soldered a couple of wires, reassembled the battery without the circuit board and charged it with the laptop battery charger. It worked fine. With the second battery, I took pictures so you can see the process.
Step 1: Needed Tools and Accessories
#10 Torx bit and driver
Needle nose pliers
Hot glue gun
Small piece of black wire (about 4")
Universal multi output voltage laptop charger with 20v output option
Two small red and black insulated alligator clips
Step 2: Open the Case
If you have a #10 security torx bit, use it to remove the 4 screws from the case. If you only have a normal torx bit, first use the scratch awl with enough pressure to break off the little pin in the middle of the screw head. You might have to come at it from several angles but it can be done. Then, you can remove the screws with the normal torx bit, pop the top off and remove the two plastic locking tabs.
Step 3: Remove the Circuit Board
First, pry up the white plastic charge connector support so it is loose. Remove the 4 small screws holding down the circuit board. Cut the four thinner wires from the outer edge of the plastic battery holder (three red and one blue). Cut the black wire at the charger connector terminal, and also cut the blue and red wires (that are visible from the same side as the black wire) at the connector terminal. Do not cut the red wire that is opposite the black wire at the connector terminal, but rather cut it at the circuit board. Desolder the battery connector tab from the circuit board as shown. Pry the circuit board up from the tab you just desoldered and tilt up the circuit board. Cut the red wire from the bottom of the circuit board. Remove the sponge tape holding the thermal protector on one side of the battery case and remove the circuit board. Separate the charge connector stand from the circuit board.
Step 4: Rebuild the Battery
Set the charge connector base back in its original position with the two pins in their respective holes. Use the glue gun to fill in the space and to attach the other two legs to the battery holder so it will stand firm. Strip the red wire from the charge connector and the other red wire from the battery pack. Place a piece of shrink tube over one wire, solder the two together and cover the joint with the shink tube. (I know. That's a duhh.) Find another piece of similar wire (black if possible) and solder one end to the charge connector where you cut the original black wire. Solder the other end to the tab on the battery pack that was desoldered from the circuit board. You are done with the inside work. Replace the spring tabs on the side of the case, snap the top back on, carefully aligning the charge connector terminals and replace the screws.
Step 5: Build the Charger
I live in Mexico and bought my universal laptop battery charger on Mercadolibre.com for about $10 dollars. Yours may be different depending on where you live, but there are cheap universal laptop chargers (made for lithium batteries) readily available. The charger must have a 20v output position on the selector since these are 19.2v batteries. Mine fortunately came with a two pin connector wired to a multiconnector, so I simply cut the wires at the multi connector and put the red insulated clip on the positive side and the black clip on the negative side. Yours may be more complicated than that. The trick it to have the alligator clips on the output side with the positive and negative wires clearly identified. Check the wires with a voltmeter if in doubt about which is positive and which is negative.
When your charger is ready, make sure it is set for 20v output, connect the red, positive, clip to the positive terminal on the rounded side of the battery charge connector and the black, negative, clip to the negative terminal on the flat side of the battery charge connector. Let it charge for almost an hour and try it out!