Earthman
As I found out over the years, the boat electrical system is really a key element of the vessel and of enjoying your time aboard. If it is well set up, your life is way less stressful…as you are already discovering.
I was in exactly the same situation as you when I bought my boat in terms of what was what with the charging and electrical system on board. There are still a lot of guys who have forgotten more than I know about marine electrical systems, but I am pretty up to speed on my own boat’s configuration.
First step is to explore and see what you have. I realize you probably have half a dozen priorities at this point but one thing you should absolutely do is start whiteboardung your set up. Get all the parts identified and get the documentation specs for those parts, including batteries. The internet is a mother lode of data on just about everything including old and obsolete stuff.
I find this research kind of interesting and you learn a lot about your boat by doing it. Trust me, you will find out all about your tankage and bilge pumps and wiring and on and on as you explore the power system.
AGM batteries can be a bit different between mfgs in terms of voltages for charging , float and so on, that is why it is useful to know exactly what you have. You can go to the mfg website and obtain data for your specific batteries. This will give you charging profiles and appropriate voltages and temps, etc. for all phases. Print that stuff and start a system manual for the boat, continue with the rest of the electrical gear.
Typically the boat will be configured with a house and start bank of batteries. On my boat I rarely use the house bank for starting. Only if the start battery has issues and very mindfully in that case which is rare. You can screw things up inadvertently connecting your good house batts to a bad start batt. The house bank is dedicated to utility power aboard the boat but I think should only be used for starting in emergencies. The start itself draws a lot of amperage but for every short duration so rechargingthe start usually does not require a lot of power. And if the boat isnt starting right up?..well there is another discussion… hahaha.
A battery monitor properly configured, will give you insight into how the bank(s) are doing with respect to state of charge, temperature and a variety of other useful data. It is especially helpful for the situation you found yourself in ie how much are my led lamps drawing and how much ampacity do I have left in the batt(s) constantly updated in time. It will also tell you how long the batt will support whatever load you subject ot to. Very useful.
A regulator, properly configured and coupled with an appropriate alternator, will allow you to tune battery charging precisely to thr mfg charge specifications you printed for your manual. It also provides useful info regarding performance of the regulator and the alternator.
I assume you have the yanmar 2gm20f motor? If so, it was originally equipped with a 35 amp Hitachi self regulated alternator. I think I have that amperage right. This internal regulation was set up for lead acid batteries and is not configurable so if you are charging AGMs with it you will want to verify the Hitachi regulator output is properly compatable with your AGMs which you can check in the boats electrical manual you are preparing.
So I could write a book on the F30 electrical stuff, 90% of which would be pretty accurate. If you pm your phone # we could chat about all of this and I might be able to help with other questions i have owned my boat for almost 25 years now so i have seen and fussed around with just about everything at this point.