I signed up to share some information that some may find useful, feel free to relocate if this is not a suitable sub.
So I've been an electric car owner for about a year and a half now (Leaf ePlus). We were a one car family but my wife needs to use it more often than before so I picked up a 2nd hand 2012 iMiev at auction. I understood that that was in and of itself a bit of a risk as there is no test driving etc. But there was enough battery to turn the available cars on and see RR at that battery level and do whatever static tests I wanted. I have a OBDII bluetooth adapter but canion only shows battery capacity and nothing else when using it (37.7Ahr). I would have known about the miev's pickiness to adapaters if I'd have found this forum a little earlier.
Anyway, wife prefers safety features etc in the Leaf so predictably I'm now using the miev for commuting (easily within range). I got the car and was commuting with no big issues, but then I decided to charge to full to see what sort of range I could expect. I put the car on my charger and came out in the morning to find it had only charged to 13 of the 16 bars on the meter. Tried plugging it in again, but charging finished within 1 minute. I didn't think that boded well, and after some internet searching I found this forum. Similar threads all pointed to a bad cell, and I was prepared for the worst.
Next step was taking it into a dealership for a battery checkup (overnight, free loan car). Result: pack health 79%, 82% after balancing, BUT 1 defective cell identified. They told me immediately that the defective cells were under warranty for 10 years so it would be replaced, I just had to have a checkup to ensure the car hadn't been abused as I wasn't the original owner. The checkup is a list of government recommended annual spot checks which I'd already had, but not at a dealership so they do it again. Including the battery check, total cost around USD$150 (but in Japan, not US). They say they'll be in touch when they clear things with Mitsubishi and know when they'll get the cell.
About 8 days later they get in touch to update me on the cell. They wouldn't be replacing it, Mitsubishi had authorized a full battery replacement (under warranty for 8 years). At that time, they didn't have the battery schedule yet, but would be in touch once they knew. They'll need the car for 2 or so days, but will provide a loan car again.
5 days after the last update they call again. The battery has been sourced and would arrive with them in another 4 days. The batteries are heavy so they want have my car when the other battery arrives so that they can send the defective pack back on the same truck. They wanted me to drop the car in the day before and leave it with them for 3~4 days. I'd have free use of a loan car during that period.
So 16 days after the battery checkup I handed over the car. 4 days later I had it back with a brand new battery. All in all, 20 days from battery checkup to battery replacement. With just over 3 months left on the 8 year warranty, I have an as good as new iMiev.
RR of defective battery: 85km @100%, after balancing 92km @100%, after battery replacement 112km @100% (value when I picked it up)
This worked out very well for me, but it was a big risk and could just as easily have been money down the drain. But for anyone with a 2012 iMiev, it might be worth getting a battery checkup done.