Our 2 year old Zoe had an advisory from its 2nd service to say the rear brakes show signs of them having overheated. They went on to say I should have this checked as it may have hardened the brake pads. What surprised me is the car has only done 11000 miles.
Was told if we wanted to book it in to have this examined, any Root cause of dirt etc would not be covered by warranty. If faulty components were found it would be covered. They didn't push this at all which made me suspicious, so I had a look myself...
First thing I noticed after jacking the car up, and with the electric handbrake off, is the wheel took a bit of force to turn it by hand - it should freely turn with little force, so...
Took the brake pads off and found their Locating lugs to be noticeably rusty, hence causing them to be a tight fight in their guides. Also took a wire brush to them to scrape off the rust and gave them a light coating of grease.
Note you need to remove the electric motor handbrake assembly, just 2 torx bolts and it pulls off, to allow the floating brake carrier to be removed allowing the brake pads to be removed.
This begs the question - would you expect this rust to be warranty or 'wear and tear' with only 11000 miles?
I once owned an alfasud which also had rear disc brakes on a smaller car. I found that lack of use was the problem and I also had calipers sticking/seizing which is what it seems you have. I have seen YouTube posts with a mechanic warning the EVs in general need regular brake servicing to keep them operational as regen braking does most of the work. Therefore rear discs on a small EV seem to carry a lot of risk unless freed off and cleaned at intervals.
Well, brake pads imho are not covered under warranty and are classed as a 'consumables'. I think I would clean it all and lube it with copper grease and be happy I've not parted with and cash to Renault.