The battery on my old drill was going dead way to fast so my solution was to make it work on a SLA battery. I checked and there are a couple of similar instructables but none that have the option to use the original battery which was important to me. Caution: I am not responsible if you ruin your drill
wire (16 gauge or lower)
blade connectors 2x
heat shrink tube (optional)
drill bit (21/64 if using same plug as me)
wire stripper (recommended)
hot glue gun (optional)
Step 1: Disasembly
simple enough, just remove any screws and other parts holding the drill together.
Step 2: Planning
Now is the time to figure out where things will need to go and how to get there
Step 3: Drill and Wiring
This is where it all happens, you will want to drill a hole in the case and then thread in the connector if you you are using the same type as me. It is very important that you get the polarity right, at best the drill wont work but at worst it could probably kill the drill. From there you will need to solder on the wires and if you plan to now is a good time to add some hot glue. I did this to both insulate and reinforce the connection area. After thats all done its a good idea to test it out before reassembly.
Step 4: Final Notes
The drill i used is 14.4v and the SLA is 12v the closer your drill is to the battery voltage the better it will perform. I have no idea what these DC connectors are rated at but i know that the drill can go up to 18 amps! It may or may not last. Also the longer the wire you use the more voltage drop you will get, i went with 10' and you can tell it goes slower so larger wire is recommended. Other things you might want to consider is a car adapter which is easily made also a fuse might be a good idea, if you do use a car cigarette lighter make sure it is rated for at least 20 amp or more.