Need to trace wiring
and understand the system. While many boats are "typically" connected electrically, you have some "enhancements," notably the inverter charger. Those well made chargers generally have only one output, a big #2/0 set of wires which should go to positive and negative distribution posts before they go to the house battery bank. The starting bank is usually charged with a combiner or echo charger, the echo charger being superior in that it does not overcharge the start bank; the combiner will overcharge the start bank unless disconnected. Your OEM alternator will most likely do little damage with its internal regulator and tapering charge regimen. Given the size and quality and value of your investment, it may be wise to "wise-up" and stop being "stoopid" and learn about the electrical system. A $50 investment in Calder's Boatowner's Manual could save you a lot of grief and improve your electrical system.I say this because I believe that it is unwise for any of us to provide you with specific guidance because we do not know, personally, just how your boat is wired, and all we can do is provide generalities and suggestions based on what have done with our own boats. Who knows whether you have isolators, or a combiner, or just what switches you have and use. We don't know if your alternator is wired to the C post of your 1-2-B switch or to a PDP.Your problem is, most likely, NOT your batteries or your chargers (I/C or alternator) but rather the way the SYSTEM is wired. A little bit of wiring, appropriate switching or relays, and your personal understanding of the way YOUR boat is assembled is what you need to undertake.While Don is right about the start bank charging, I believe that there is no need to replace your Heart I/C, it's a great unit if wired properly. If the switch Don suggests works for shorepower, there's no reason not to make it work while underway, too.This is a perfect example of why you should learn what you have, since this subject is way too complicated to answer in this type of board.You can also read up quite a bit with West Marine's Advisors in their catalogs and on the web, and read about alternators, chargers, etc. on any Catalina Association website. An example from our C34 'site is: http://www.c34.org/projects/projects-electrical-system-upgrade-2.htmlIt discusses the entire system and includes a wiring diagram. You would be well advised to start tracing and drawing our your own wiring for a good understanding of how your boat is currently hooked up and what changes may need to be made to make it work without overcharging your start bank.Additionally, from an article I wrote in the Nov. 2006 Catalina Mainsheet magazine: Alternator Output: The older boats with only one 1-2-B switches are usually factory wired with the alternator output to the “C” post of the switch. This means that the switch was actually used for two purposes: (1) which battery bank(s) the alternator charge goes to when the engine is running; (2) which bank is chosen for use for DC power. We changed that. We moved the original alternator output FROM the “C” TO the “2” post (our house bank) of the switch. The Combiner charges the start bank without having to use the 1-2-B switch for selecting alternator charging output ONLY because we moved that connection. {Before we upgraded our alternator and ran a new wire from the alternator to the PDP:::] The revised alternator charging path was from the alternator through the Auto-Mac to the “2” switch post to the house bank, using the #4 OEM red wiring. IMPORTANT NOTE: You cannot simply move the alternator output from the “C” to the “2” post without a Combiner or Echo Charger type relay equipment because the start bank would not get charged. Another way to put this is: If your alternator output is wired to the C post of the 1-2-B switch, and you do not have a combiner (or equivalent), then you have to start the engine with the switch on B (ALL) because this would be the only way to charge both of your banks from the alternator.As I said, it's complicated and this just begins to touch on the subject.Your boat, your choices.