1) Filling your tank....Keep filling until the water starts coming out overflow lines or back out the gravity fill hole. It can take a long time. I usually walk away to do other things and listen for the splashing water sound as a signal that it is full. If you don't have an enclosed underbelly you can always crawl under and look too. Give the trailer a shake first so you can see the water sloshing around.
2)Your trailer will have a constant draw on the batteries. Usually propane and CO detectors. They can easily draw down your battery over a week or two if you let the trailer sit. One option if available is to keep it plugged in at all times while in storage. Another is to completely disconnect the battery either with a switch or remove a cable. If your battery was completely drawn down it is likely toast and time for a new battery. It will work fine while you are on a generator or plugged in but it won't hold much of a charge anymore.
Ooops, I see Jmooney is a faster typer than I am!
2014 Jayco Swift 281BHS
2015 F250 XLT 4x4 Crew Cab, Short box, 6.2 gas
Solar powered! The trailer not the truck!