No the voltage doesn't drop sharply. I had actually purchased the 750w motor from electro bike world. Their support was good and they were responsive. I ended up having to order some spacers in order to mount the motor properly.

I did find this controller but it looks like some rewiring would be involved. I actually have XT90 connectors but not sure what else I would need.

https://electrobikeworld.com/products/35a-controller

It seems like it might be easier if I start from the beginning. I'll try and make a long story short. I first purchased a 2021 Rad Rover but then I also purchased a used 2016 Rad Rover off Craigslist. Both bikes were running fine but we noticed that the battery on the 2016 model was not lasting very long. I didn't know anything ebike battery voltages or amps and I had hard time finding a vendor that would ship to Hawaii so I ordered the biggest battery I could find from a vendor that would ship here (my bad). I installed the battery and the battery was working fine and then I came across a Rad Power upgrade kit. I ordered that and installed the new controller and LCD myself and everything was working fine still. I then ordered the 750w motor and also installed that myself and everything was still working properly. We took the bikes on a camping trip and we were going up a steep hill on muddy ground and as I was peddling with PAS on and the motor just cut out completely. I took it to Krank Cycles and they charged me $100 but they were unable to diagnose the issue. I did some research and it appears the issue was most likely a hall sensor that was burnt out. I then took it to Maui Sunriders bike shop but they refused to repair the motor but said they would swap out the motor if I purchased a new one. I then purchased the 1000w motor from Big Game Bikes and dropped off the bike with old motor still installed and new motor still in the box. I asked if they could swap out the motors and test the hall sensors on the old motor. The rest of the story was in my original post but as I mentioned the battery was the first thing I replaced and was working properly until I had the installed the 1000w. I'm not sure how it would be incompatible if it was working previously.

Before I picked up the bike from Maui Sunriders I did offer to purchase a new controller but they don't carry those. I explained that I would look online and he said that I would need to find one with Juliet styles plugs and requested that I pick up the bike in the meantime. I think he might have rewired the original connector but I can check when I get home and post a picture. Would you be able to recommend a controller that is compatiable with a 52v battery?

The battery was working fine with the previous 750w motor I had upgraded to. Does that make a difference?

Thank you for quick response. I checked my C12 setting and it is set to 4, which I think is correct. I've attached some pictures with my settings and the model number of my battery. Going to look into what needs to be done to balance a battery next. The battery is not OEM and is about 3 years old.

I've ran out of options and this is my first post to this forum. I have a 2016 Rad Rover and had purchased a Bafang 48v 1000w Rear Hub Motor (L1019) due to some issues with my 750w motor I had previously upgraded to. The 1000w motor was not a drop in replacement like the 750w was so I took it to a local bike shop. They had my bike for about 2 months and they were unable to get it working properly. They had tried to charge me almost $300 for the "repair" but they also threw away my other motor, which I had asked for a diagnostic on. They ended up only charging me $100 but I still have a bike that isn't working. I brought it home yesterday and when I pull the throttle the tire spins for about 3 seconds then cuts out. I'm running the RadPower Upgrade Kit from Bolton / Area 13 ebikes and the motor was purchased from Big Game Ebikes. Any suggestions would be helpful. Please let me know if you need additional information.