Agree that actual specs would help.
But even if you have super high quality Lifeline AGM's, Group 24 are only going to hold about 80 ah apiece (we're talking of the various lead acid type batteries here, such as flooded, AGM, or gel.... not LFP).
3 batteries at 80ah apiece is 240 amp hours. So about 120 ah usable even if they are the best kind. That's a pretty minimal house bank for most people (not everyone, but most).
BTW, if your boat has the under-counter style fridge, you probably have something no larger than 130 liters or about 4.5 cubic feet. Perhaps using the Danfoss/Secop BD35 compressor. If it's a "drink" model it may not even have a freezer.
I've been running a fridge of that size and living basically on DC power for some years (solar), so I have a pretty good idea of how many ah it takes per day. Obviously this is dependent on ambient temperature, and your installation; but I'd say something from 30-60 ah per 24 hour day would be a reasonable guestimate (presuming not in the tropics). I just mention it because some others who estimate more may have larger trawlers with full height refrigerators that have larger freezers. Of course they draw more.
Another thing to note is that due to something called Peukert effect, the batteries react worse to a large load/small time than they do to a small load/large time. So for example running something that draws 20 amps for two minutes, exhausts the batteries more than running something that draws 4 amps for 10 hours (even though both add up to 40ah). Just a note in case you are using anything like a microwave, or anything that makes heat via electricity.
Voltage is not typically a very reliable way to gauge your state of charge (SOC), especially if you are relatively new to the care and feeding of a house bank. Reason is that unless the bank has been resting (no loads) for many hours it won't be accurate. If you are using power or charging then the bank is not resting.
Hence using a battery monitor is useful. They either use a shunt and count amps, or there are some that do use voltage but they do it by checking voltage thousands of times and applying an algorithm. (For example, original Smart Gauge.)
Given your plans, I would say you are most likely going to want to re-do your battery bank completely, and possibly parts of your DC system (depending on what you have now). But as you say, you can get through the rest of the season on what you have, and then take your time researching and getting squared away for your loop trip (sounds fun!) over the off-season. Pressure's off on "not wrecking" those batteries if so
I don't know the details of your situation or setup, but until you find out your specific details, I wouldn't assume your system is set up for a relaxed loop trip. I only say that because I can't imagine doing a big electrical job for someone and not noticing that the main house bank is a bit small (or at least mentioning it).
Of course a lot depends on how you travel. If you go marina to marina and so are motoring most days and plugged in most nights, then you may be fine. I'm an anchorer so I approach my system with that in mind. Many ways can work, just depending on your style. But as you are realizing, knowing what you have and how it works can make things a lot more enjoyable, whatever your setup or boating style.
