Lots of good advice above. Something of concern: "Now for some reason the previous owner connected up a few devices that are on all of the time."
Yeah, those previous owners.... made sense to THEM at the time...
What to do? Me? Once I had her back home (in your case) I'd disconnect everything. I mean everything. (Have to buy an iggy ice chest for cold beers.) And I'd isolate one battery to one charging system, then later hook that bat up to a load. See what happens. Repeat for each bat. Get a base-line for each bat on that one charge system. Drag 'em to a bat place if needed for charging. Might end up throwing away some of those bats...
Then I'd trace ALL my wiring
while the bat(s) charges. Bears repeat from above: You'll be best off knowing where every wire goes. Trace them out and make a booklet. Flashlights, ohm meter, and a helping friend if needed. Trace those wires! Might find things that need rework. Yeah - some wires might be behind woodwork or otherwise under cover. Tough. But check.
If you didn't hand-wire the boat yourself, then all sorts of things are suspect. Example: somebody splices two short lengths - and when you finally get the boat the connection has corroded. Bummer.
Note this: On my boat and only discovered while underway, once found a pwr line attached to the main pwr distro panel at one end and to nothing at the other - just dead-ended in the lazarette. But it was run near the steering
cable (under the floorboards aft) and had rubbed through. Depending on boat heel, the cable would short out and suck power from my bats.
THAT decided me to trace out EVERY wire on the boat. Bunch of cable ended up in the trash; they either went nowhere or were non-marine wire. My vessel's "previous owner" will get a jolly good right cross to the chin one day...