You need a fail-safe. That happened to me and a fail-safe saved my car. Also saved me from a long walk.

I used to use 4 AA for the receiver. On another occasion, I took a jump and one of the batteries popped out breaking the connection.... the buggy took off. It almost took out my wife who was sitting near by. A peice of Hockey tape fixed that issue as a fail-safe wouldn't have helped as it needs a power source. I later upgraded to a 6 V.

BTW, a 6 V made a world of difference in my Himoto. The turning is much more responsive and the acceleration is crazy... especially off the start.

Next time you pick up some spare parts, pick up a 6 V too. You won't be disappointed.