I bought a new Ranger RT178 in June 2021. I keep it in a boat storage facility that has electricity in the unit. Over the first several months I had problems with a battery going dead. When the GFI would trip in a storm if I didn’t get by the storage in a day or two one of the trolling motor batteries would be dead. Replaced the battery. Now the cranking battery is going dead in the same scenario. Seems to me the boat may have wiring issues from the factory. I need a recommendation on who to take it to that is really good at troubleshooting electrical issues. Who would you take it to?

Install an on off switch, seems like something is staying on and drawing power

Does your boat have livescope? If so, the GLS10 box is always on unless you have a switch installed to turn it off. If you don't have that then I agree with the above, something is staying on.

Just a spit ball here but I just recently had an issue where one of my trim switches went bad and caused the power trim to run intermittently. I actually found it when I walked out to the boat one night and the power trim was running. So unless you catch it at the right time you'd never know it was happening.

Are you using the vent fan, dry dock, whatever it's called? If you lose power that blower motor will drain your battery. Another possibility is if you have an Ultrex or Power Poles. Like was said above, use the master cut-off switch.

And add a Perko switch to kill power to all electronics.
On my 2014 Skeeter FX21, I had the same issue.
The master does not kill everything.
I throw the master,Perko and trip the TM breaker, problem solved!

Yep. Turn everything off with a main switch. Believe it or not, but depth finders pull current when their off. The units are always on waiting for the power button to be pushed. Also isolate your trolling motor from your batteries when they're charging, this is a big question mark and many people have different thoughts on this but I isolate everything.

YUP!

Thanks guys. Perko switch installed.