Many years ago I worked on a project where we had battery backups. Some of our batteries were NiCad and others were some weird metal combinations. The NiCads were charged and discharged as a unit but the weird ones required many little chargers that monitored each individual cell. It was the only way to ensure each cell didn't over charge or discharge. If they did over charge or discharge it ruined the cell.

My point, Ioannis, is that I agree with your last post in that you'll need to treat the cells individually. Not only for safety but for efficient charge and balanced discharge.

It wouldn't surprise me if the car monitored the battery using some proprietary bus scheme. Seems like cars get more and more complicated each year. Not necessarily better just more complicated.