My flashlight batteries don't receive any charge when they're hooked up in series in my flashlight.
I think the issue started way back when people tapped off of their low side battery to draw their 12V power. This caused the low side battery to draw down, resulting in sulphation. I have heard that the high side battery can become overcharged in a system where there is a bad low side battery, causing the high side battery to boil over.
This is how I have hooked up my system, drawing from the low side battery so that I can draw large transient 12V loads when I need it. I have my Solar Converter shunting current in load balance mode, and it keeps my batteries fairly equal to each other. I then flip my switch to turn it into strict convert mode when I need to leave my vehicle for days at a time, to avoid drawing down my batteries. My system has been very happy for almost two years this way, using two Interstate Workaholic batteries.
As I've stated in my post, mine is more a gut instinct type feeling. I have read on one website that concurs with your theory that batteries hooked up in a bank, whether in series or parallel, act as one battery, and that in series, a bad cell does not necessarily cause any problems with current flow. I'm going to be doing a bit more reading.
