Yeah, same deal here. If the battery was anything too horrendous, it would either be stock still or not reporting via LeafSpy. That's what mine did and the 'fault' as far as the vehicle was concerned was that the on-board charger wasn't communicating on the CAN. It wasn't communicating because it was toasted and pulling the internal supply voltage down, but the car didn't know that.
That seems like it's probably the best way forwards. It's a pretty easy swap (biggest pain is the coolant and replacing the seats). The HV connections can be a bit of a fiddle to get them to unlock, but just check the service manual and it'll explain it.
That response from Nissan Takapuna sounds pretty good, actually, I'm impressed. I'd always rather deal with someone like that than get the whole run-around, meaningless quote, etc.
Interesting that they have a bit of a problem, so far I was still the only person I'd heard of replacing theirs, so I was hoping it was a bit isolated.
The braking issue is just that it seems to randomly get really touchy and hard to stop smoothly. I've seen quite a few people mention it and seen it get blamed on 12V battery issues, firmware, sticky rotors/calipers, all sorts. It's not enough to be an issue to drive, it's just a little annoying. It normally clears up for a bit if I come to a complete stop and give the pedal a good long/hard/slow press.
Anyway, like I said, try pull the cover off once you get it out and grab a few photos. If the controllers look the same then there might be a way to salvage the old one, once you've got a working one to test against.