Ideas?? On-Board Battery Charging System tripping circuit breaker

Just got back from Canada yesterday. On Friday, got caught in a driving rainstorm for the better part of 3 hours while fishing a river up there. Naturally, tried to dry her out, but ultimately had to put the canvas on over a wet boat and trailer it 12 hours in 90+ heat on Saturday. Took the canvas off Saturday night (the boat is garaged, always). Note that it charged the batteries just fine Friday evening before the canvas went on. On Sunday, opened all the compartments, tried to plug it in for a trickle charge and tripped the breaker--something shorting out. Checked the battery compartments--ignition battery looked a little wet, so pulled the boat out into the sun, let it dry out for a few hours and tried again. Tripped again. Can't see any water, and the charger and the compartment it's in look and feel dry. This is a 4 bank charger, 3 AGM trolling batteries in a 36 volt system with one "wet cell" ignition battery. This is the 5th season for the batteries and charger. Never had any problems before.

Any ideas on how to test what's happening and where? I'm going to let it dry out for a few more days, but I don't think it should be doing this.

I have no ideas as to why its happening, obviously a short somewhere. For a start you could try to unhook each lead (or pull the inline fuse)one at a time and see if maybe you can at least find the problem spot.
My battery charger died earlier this year, I never could figure out what the problem was. I just knew it wasn't right. I finally sent it to Rumpke for its last road trip.
Good luck with it.

Is this a GFCI breaker powering the charger? If so, I'd be looking at the charger plug and the charger itself. A little bit of condensation is enough to cause GFCI problems. A hair dryer can work wonders in this situation.

The GFI on the wall outlet is tripping.

I'll try disconnecting each battery in turn, which will narrow it down. But because this is a Dual Pro with 4 individual 10 amp chargers inside, it won't tell me whether it's the battery or the charger. If one bank proves faulty, I'll connect the battery to one of the other banks, and that should tell me what I need to know. Before I do any of that, I think I'll plug it into another (independent) outlet to make sure it's not a bad GFI.

It is not on the battery side, so don't bother unhooking batteries. The GFCI measures AC leakage current, so it's on the 120VAC side of the charger.

Even leaving a cord out on a foggy morning can cause enough moisture to accumulate to cause a GFCI to trip. Pulling the whole boat out in the sun with the cover off or aiming a fan into the the charger area will fix it in a day or two, but using a hair dryer on the plug will be faster if that's what has the moisture.

Trying it on another outlet is a good idea.

So I tried another outlet (a standalone 20 amp outlet I use for my table saw) and it tripped the GFI. I don't have any non-GFI outlets in the house. I also had it outside, uncovered, with all hatches open on Sunday in 90 degree+ heat--didn't help. No moisture showing in the windows, so I don't know what's going on. Called Dual Pro (the unit is 4 years old, had a 3 year warranty naturally). They offered to sell me a new one at a discount for $369, which is about $25 MORE than I can get it online. They explained by saying that vendor buys in volume. I can pick up a reconditioned unit from them for $239. I'll try a hair dryer, but I'm beginning to think there's something else going on--just don't know what. These units are supposed to be waterproof----but I'm beginning to think that's crap!