I presume you have reset the robot? The tiny hole on the bottom that you have to stick a pin or similar into for 3 seconds? Their troubleshooting guide is ridiculous and insulting but try the help tab on their app to get to the chat person, that has helped me in the past.

Try swapping the batteries between the 2 units to find out if it’s the battery or the unit that is causing the problem. It’s possible you have bad battery or bad continuity in the unit to the battery.

I didn’t realize it was a belt, I thought it was just an o-ring. I dismantled my R95 trying to find out why the LDS wasn’t rotating anymore and found the rubber o-ring/drive belt broken and slightly jammed into the rotating navigator which houses the lasers. It came out pretty easily. There is a repair place, ifixrobot.com/Ecovac but they never responded to me. It took a while and many trials but a friend has a machinists book of everything and he determined what size o-ring I needed for the drive belt based on the measurements of the broken o-ring and then found it on Amazon. It’s working well. I didn’t take any photos and feel awful for not doing so for others but the video link below does cover what I did although in a less direct manner. I will tackle the project again after I fix my Shark and post photos in sequence. In the meanwhile for the R95 DEEBOT and the LDS 002 navigator (presuming it might be used on other Deebot models), the belt is a 2-042/N7 70 Buna O-ring the size is 3-1/4”x3-3/8”x1/16”...