Slight dissenting opinion on paralleling batteries: ALL diesel vehicles generally have parallel 12VDC batteries to give the starting current necessary to start a cold diesel under compression. There is
no problem with the batteries going whacko because of this.

Point 2: Many solar panel storage batteries consist of multiple banks of parallel and series batteries to give huge storage capacity. No problem there.

Batteries will attempt to balance themselves to some extent, but careful attention to maintenance and SG of the cells will prevent a system failure from happening.

Doug