Sorry, I just saw your message today. I do the same as you, A position for starter, and B for electronics etc. I took out the original charging set up and installed a ProMariner model 1210P computerized unit. It charges which ever battery needs it, and if both do, then it does both at the same time. Amazing product and will extend the life of your batteries. Here's a link to their site -promariner.com.

Hey Jim, I have the Maxum 2300scr which I bought used and put RIGHTAWAY into winter storage so i didn't get too much of a chance to play with it. Can I ask you how your electrical/battery system is set up? I have been reading here on the site and elsewhere and am very confused re: A/B/Both switches. On my last boat I started on A (Starter) and when at anchor switched to B (House) for electronix. I am pretty certain this is correct but getting contradictory info. BUT also if I am running on Starter Battery is that also charging up the HOUSE battery at the same time? Besides plugging in at the dock, how can I keep the House topped up? Also when at the dock and plugged in, is it charging the House and Starter battery? Just the Starter? Or does shore power follow the A/B switch. Any opinions on starting and running for a while on BOTH to top up both batts then switching to A or B once topped up? (i read that running on both can be bad for batts and alternator) Thanks in advance