I don't have the battery part number handy, but they are just small 12v batteries for smaller devices like a mobility scooter. The speed control was the magic to make it work. There are three "handy" things you need to do to make it work.
1. Have a platform to hold the batteries. I used some scrap plywood U-bolted to the frame above the wheels. I used some scraps to make a holder around the bottom of the batteries on the plywood to keep them from sliding around and then used some threaded rod to make a hold down to prevent the batteries from falling even if the unit tipped over.
2. Need to get a speed control as the trigger in the drill can't handle the current. This is what I ordered off of Amazon and it has worked well.
speed control
The instructions for it are lousy, but if you have google translate on your phone you can hold it over the sticker on the top that shows the wiring and you can see what to wire to what to make it all work. You'll need a relatively heavy gauge wire from the battery to the speed control and from the speed control to the drill motor. I used 12 gauge speaker wire that has worked fine. To make it 24v, make a small jumper wire that connects the + on one battery to the - on the other, then use the remaining two to connect to the speed control.
3. Eviscerate the drill. This was the trickiest part and making sure you have access to a spare one is good insurance. As you found out, you need the exact model for the collar to fit.
- Gut the battery pack and get a DPDT switch. This is how to switch the tug forward/reverse. Drill a hole in the battery pack and install the switch. Look inside the pack shell to make sure there's clearance for the switch as there are a lot of plastic bits that get in the way. This switch goes between the speed control and the drill motor.
- Open the drill and remove the trigger. Wire from the reversing switch directly to the motor. Be very careful to not let the guts of the drill fall out. The three speed transmission is a bear to reassemble. (Ask me how I know). Reassemble the drill and clamp it to the tug.
The last part was to weld a tube for the twist grip throttle. I went to a local welder who had some of the right tubing and welded it up for me. I used about 8" of tubing to make a handle for maneuvering the tug.
I think
@flyingron suggestion of the newer drill that fits might be the hot set up. It uses a brushless motor which should have more power vs the older model's brushed motor and it has Lithium batteries that should work much better than the NiHM's in the older drill. It's not cheap, but it's turnkey so might be the easiest solution