You have an interesting story spread out over many posts.
-You bought a 36V Bagi B10 bike and they put in a 48V battery. You commented that they adjusted the display. The C961 manual does not show any settings to adjust voltage. Wonder what they did to make the battery gauge work right.
-The Bagi website also doesn't show your bike with a C961 display, Where did you buy the replacement. What do you see on the display when you say it doesn't work. What did you see when the old one didn't work.
One possibility is the controller blew up. Some 36V models cannot handle 48V long term. That would be a common reason for both new/old displays to work.
I don't know what works with a C961. I'd recommend you buy a controller and display as a combo, so you know it works. The selection will be impacted by how much room there is in your bike for the controller. You probably want to limit the current to 17A, your old one was 15A.
You should also know there are few standards for the controller wiring. It's likely the plugs may flip gender, and almost always flip the wiring order. Swapping a controller requires some electrical skills.
I know someone who wanted to do a swap. I recommended he buy a complete kit, with the display, brakes, throttle, and PAS sensor, plus a harness to connect them all. All he had to do was stuff all the wires inside his bike, and it worked great. About $120 from China. The controller/display alone would have been $90.
