From before I started going to miters earlier this year, there's been a car chair mounted on an old electric wheelchair base. Unfortunately it didn't work and didn't have a battery pack so it was hard to test. Earlier today I decided to see if I could fix it. Fortunately Shane tipped me off that electric wheelchairs often run at around 24v. I hooked it up to a DC power supply and it turned out it worked when everything is plugged in (with the power supply in place of the battery). In other words, all it needed was a battery.
Soldering the cells:
Heat shrunk & insulated the contacts
Charging the batteries:
Chair base sans-batteries
I forgot to take any pictures of it with the batteries inside and I didn't get any good pictures of it driving around (my phone crashes when I try to put it in video mode). Someone else took some video, hopefully I'll get that soon so I can post it. The chair now drives around very smoothly and has space for at least 4x the batteries I put in it for increased range. It still needs a good mount for the controls and possibly a better interface. Odds are it'll make an appearance next time miters has a booth for something.