So this is a Detroit bike e sparrow
250w rear hub singlespeed
Ive rode this bike for 4 years. The motor started cutting off going up hills and even on long extended flat sections this past year. I think a sensor, cable or perhaps the battery was going bad.

I ordered a new battery on ebay to upgrade from the stock 36v 7ah to 36v 10ah. I had to switch half of the new battery tray to get it to lock and there was a small mishap.

Putting it together I accidentally touched the metal plate to the 4 pins of the battery tray bracket with the controller circuitboard housed inside and there was a spark, oops! Luckily it throttled up fine after getting it together, phew!

Anyways I adjusted the brake cable tension, put new chain on and went to go test ride with the new battery and it no longer applied power. So now I’m thinking maybe it is a wire/sensor since I just did the brake adjustment. I wiggled the wires that go internally through the frame by the bb to the battery tray and to my surprise I got throttle and pedal assist back!

I got on the bike and there was a lot of power! Unfortunately the rear was making a grinding noise, Im not sure if the brake rotor was rubbing the caliper from the new chain being too long or if for some reason the hub motor wasnt paired with the new battery well and maybe it affected the motor? I got off the bike and throttled to listen to the rear and there was no grinding, I got back on and there it was again.

I switched my battery pack back to my old one to see if the new one was just too powerful for the hub motor and wow I’m not sure why but my old battery was feeling twice as powerful like it was new again?! Maybe a wire was loose this whole time and that wire I moved to get it going again fixed a connection and nothing was wrong with my old battery?

Although it was still making that grinding sound, I’m just going to assume its my disc brake rotor hitting the caliper when I’m riding and forces are applied with my weight and hopefully not immediate motor damage. I really need to take a link or two out of this chain to shorten its length this is the first time I’ve installed a chain by myself and not a bike shop.

All of a sudden the power abruptly stops even though its still powered on and lit up.

I go back to troubleshooting by turning it off and on and applying throttle it moves the wheel like a centimeter occasionally. Wheeling the bike backwards and holding throttle its also resisting for a few seconds? No matter how much I wiggle these wires, switch batteries or adjust the brakes it wont give me back my pedal assist power or throttle.

I don’t know whats going on with it, but here are my guesses

1. My brake sensors are now for some reason stuck on.
2. Could there possibly be a short in the wiring or a damaged wire?
3. Did the motor randomly strip internal gears with the new powerful battery? (Doubt)
4. Did the spark I saw from the not fully discharged controller cause it to have issues. (Doubt: it still lights up normally and it did ride for a bit)

I’m very worried a bike shop is going to charge me an arm and a leg to fix this when it probably only needs a minor adjustment by an expert. Does anyone here know what I should do? The bike throttle lights come on like normal the throttle gives it a tiny burst of energy to barely move the wheel at all like once per power cycle, it resists walking the bike backwards when throttle is held, theres no burnt smell, Ive hardly ever been caught riding in the rain, the batteries are charged, the brakes are not applied.