[Rez]

A spin brush with six 1.2 to 1.5v cells *should* be okay.

Neuro says the stock spin brush motor pulls 0.28A which should be fine. Six 1.5v cells, or 9v should be okay. I've heard various reports about what the electronics can handle, anywhere from 9 to 18 volts, but if I were you I'd keep it around 9.