Puffindog

No, thanks for your response anyway.

I recently bought a used ebike for my wife, worked fine for a while. The battery condition display on the bike then went suddenly to a single bar from full. I thought the battery had failed. I'm an electronics engineer and I took a good look at the battery. The 10S pack (nominal 36 volt) gave a voltage of 40v (no load)., each cell pack at 4 volts or thereabouts( Fluke DMM). The push-button battery level on the battery showed full also. Charging is what you would expect, 3 miles (10mins) hilly trip at full assist takes about 1hr to restore with charger. Charger in at 42volts and full shows low on the handlebar display as well. All the voltages on the BMS look correct. The BMS looks like it sends battery status to the control box as -ve pulses every few seconds (scope). The control box sends the same format digital info the display, presumably with additional speed data as -ve pulse. The only thing I would say is that the d.c. voltage on the data lines is about 3.2 volts, I would expect this to be 5 volts which is the norm for data comms. All connections checked, clean and good. Any ideas (I have no circuit diagram or schematic for the system) how I proceed? Would you have to replace BMS, Control & Display all together to rectify the issue? Bike still works fine, just annoying the "fuel gauge" is flakey. There seems to be not much technical info available for any ebike system