Huge Problem!!!!!
 

I'm somewhat new to this and did a dual cell mod to my zz. It worked for awhile and was really fast. One day it started going forward and didnt stop even if the controller was off, now nothing works. Can someone help me?

i think something short circuited, like the batts were bypassing the pcb automatically and it burned out the motor or something but im not.

Gonna need more details: Where'd you put the second cell? Make sure that the bare parts of the cell are not touching the PCB or the pieces of metal in the chassis.

i had the second cell in a series going out the back window. I think maybe it was touching the pcb, is there any hope?

Recheck all of your connections to make sure there is no contact with components. Have you tried to run it anymore?