I'm glad you uploaded the near miss to "Upride CC" - we need to call out more dangerous drivers. Once you figure out the battery post your guide to help others!

I've seen a few e-shifters for sale on facebook, and there are guides on how to fix the electronics so I'd probably go that route. The main problem I can think of with changing to the 8 speed is you'll need to deal with e-shifter wire and you'll need to route the gear change cable on frame. Good luck!