Hi there,
We've got one, I built it from the plans, out of MDF (cheaper than the fibre glass jobby that he sells!) It uses 2 85amp caravan type leisure batterys. They seem to last quite well, the only time they ran out was recently at a Discovery Owners Club camping weekend, where it saw a lot of use in a short space of time :)
I also rigged a remote kill switch so that any adult in charge has control of what to let the kids crash into :lol: