YorkshireYankee - we have a contraption that converts from a car battery to an ordinary 3 pin outlet - you'd have to PM Manitas to find out voltage, duration and recharging abilities... if it helps, it's yours for the weekend.
Failing that, we could take it in turns to drive you round the car park all night with the car lighter adapter on!!!
Do hope to see you there... I'm curious about this machine of yours now!