Why 10-12 volts? The Z-750 brick I'm using puts out 21 volts and the Z-1000 puts out 18 volts (I think). We're told not to use the controllers with the bricks when plugging them to the TIU, so there's nothing to reduce the voltage coming out of the brick.
Seems kinda odd that I'd have to put the engine on a separate piece of track with another power supply just to charge the battery.