Hi Delta, M2S sent me a new battery free of charge.
Long version: My new KUSH R750 was shutting down after 3 bars without warning. I would guess the range is satisfactory of course it depends on rider and conditions. IMO range and performance was within normal parameters. However I would never saw two battery bars or less because of sudden shut down. I sent M2S a video clip and never heard from them* (see below)
A month later... one day I got a surprise tracking number from M2S. I never ordered anything and didn't know what to expect. It was a new battery. Same 48v 16AH spec as my current. I did not ask for the battery so obviously it was free and a nice surprise. The new battery works and I get 2 bars when low on juice therefore I'm happy to know it's not the controller nor computer issue. So now I have 2 batteries and the faulty one I would use for short trips as it's still usable. However comparing the two I think the faulty battery is a little low on range.
* Full disclosure: I use my work email when communicating with M2S. We have filters and I noticed a M2S message in my Spam. I caught it after quarantine but is was already deleted... so I cannot say if they responded or it was a 'bounce back'. I will give M2S the benefit of the doubt and assume they contacted me.
I also have a 'noisy motor' problem (with video clip) and I have not heard from M2S. It's possible they contacted me but I've put this problem aside because the bike still works great and it hasn't affected performance nor durability (5 months 1,500 miles). I love my M2S KUSH R750! Very fast and the 'live' throttle at 0 assist level is awesome. The bike is both fun and practical and I've relied on it for both. Hands down one of my great life purchases.