So if you have a battery powered drill, one day you will find the battery pack dead and unable to charge again. I wasn't willing to pay the price for a replacement battery, but just couldn't trash the drill. Once I bought some new cells, but found them the wrong size to fit in the case. I did have a battery from an alarm system that had plenty of power, but it was just too large. So I decided to add a short cord from the cordless drill to the alarm battery, making it a semi-cordless drill. Here is how I did it.
Step 1: Break Open the Case.
So open the battery case, keep all the parts and screws. Notice where the cells are connected. Make a note of it, or take pictures. Then trash the old cells ( recycle properly please ).
Step 2: What If You Forgot?
So you didn't make notes or take a picture of the connections? Use some test wires on the drills terminals to find what works. Now make some notes!
Step 3: Add Wires to the Old Battery Pack.
Using your notes connect a two conductor wire where the cells were connected. Then drill a hole in the battery case for the new cord and pull the cord through.
Step 4: Cord Relief.
To protect the connections put a wire tie around the cord so it can't pull out of the case. Make it tight and trim off the excess. If it looks OK screw the case back together.
Step 5: New Battery Connection.
I like to use spade connections to the battery. It makes it easier to move to a new battery. Alligator clips could be used for more versatility. If your drill runs backwards, just reverse the clips.
Step 6: Ready to Drill Again!
So there you go. You have a new short cord on your old drill and can now use just about any battery to keep working.
Please work safely and have fun.