"but I saw yesterday my car stopped at 8% SOC and many cells close to 2,8V. Really concerned... Any thoughts about that?"
Your car is doing many miles. That's what we should do with it. I suppose your car will have the battery many times at 30 ºC. So, one rate of degradation of 4%/year will be expected in your car. I-MiEV don´t recalibrate his capacity every day, takes time to do it. Sometimes if you stop with 50% SoC, after some time one bar will be not there. If he does that, it will stop with 3% SoC. But it will not count with that in the next charge. For me, your car is losing capacity with time (all cars will lose), but simply is thinking that hadn´t lost any. It will recalibrate, I don´t know when, so the best is going to someone who know to force him to do it. No problem at all with your car, just normal loss of capacity. In mine, before it recalibrated is capacity, I could stop with 14,5% SoC and 2,75 V in the weakest cell. Now goes to 0,0% SoC, like you all should know.
In conclusion, in my mind, no reason to be worried. I just see something that happened to me before, and now with almost 5 years driving it, 84.000 km, I never have been so happy with it. Just enjoy.
Riding an i-Miev since 4/2011 in Portugal, 100.000 kms.