1st time trailer owner, question regarding battery/power

My 2 cents: disconnect the old dead battery (forget trying to resurrect it, it may be boiled dry, just go get a fresh new RV (preferable) or marine wet cell battery). with Batt disconnected, get into your electrical panel, and check all the fuses. (Mine had three blown fuses on the dealer's lot!) If in doubt, replace the fuse. And keep spares around!
Plug in the 120v power and start checking stuff. Keep it plugged in to keep the new battery charged fully.