I agree with all of your comments. There are a lot of things going on in batteries and battery systems and I was trying to keep it simple to start.
The number one killer of batteries is the lack of proper charging. A lot of posts I have read indicate that the engine is run until the batteries reach float voltage and then turned off. That is only giving the batteries an 80% charge at best. Other posts describe symptoms that indicate bad connections in the system which will also prevent proper charging.
Hopefully others will put in there two cents. Maybe we can start a fight club for electricial engineers.