Battery series/parallel questions...need advice/info

This is easy. Think of it as water. Water flows to the least resistance. Water will stop flowing when you close the valve, unless there is a leak. Water goes the way you push it same as when you generate. You should check your water and add some when it is low, even in 3 months and not blame your charger like RoyB. You can always go to a Class 8 truck battery to replace both 12 v batteries.