I have two Core 5 bikes that are about 1 1/2 years old. I was going to go for a ride on the one with the most miles on it, about 2000 mi. I turned it on and the display worked fine but I had no power to the rear wheel. No throttle and no assist. I took the battery out and installed the battery from the other bike and same thing. Next I unhooked the cable by the rear wheel and got the other bike so they were side by side and hooked the good bike to the cable on the bad bike. The wheel on the bad bike worked fine so I put it back the way it was and decided to take apart the internals where the battery power goes into the bike. I pulled all the wires and the control box out and disconnected each connection and reconnected each wire. I took the battery and plugged it in and the dammed thing worked. Must have been one of those connections. Hope this info helps someone.