Help me understand my charging system...

I have an '08 X-Star that came with two batteries, one starting and one accessory. On the battery switch, it has an OFF, ON, and CONNECT ALL setting. I added an additional accessory battery and a 3-bank on board battery charger with one lead going to each battery. Im running a pretty large stereo that I play without the engine running, and I would like to add a third accessory battery. My question is, when my engine is running, with the switch in the ON position, will my alternator charge only my start battery, or will it try to charge all four batterys? Im not trying to charge all batteries by the alternator, but I will plug the boat in every night. Or, should I look at getting a larger alternator that will charge all batteries? Thanks for your help. -Ryan

I got my hopes up thinking this was THE "Ryan X-Star," dang!

I'm not an expert at this sort of thing but I believe if your batteries are ran in parallel you'll be charging all of them. Not sure how to work around that, I'm electronically impaired.

Haha, no. I'm 29 and bought my own X-Star with my own cash.

Any others info....?