I occasionally get a small leak at one of the PEX fittings, typically at a faucet. Vibration during driving can do that, and a couple times a year, I hear the telltale burp of the pump in the middle of the night. Although the PEX fittings should never be tightened more than hand tight, I "have" used a pair of pliers on one to give it just a bit of "extra" on one particularly troublesome fitting.
As for the pressure on the system without battery; did you release all the pressure when you shut everything down in February? If not, then the system may very well still be pressurized (although a leak would eventually release most of the pressure). Open a faucet and let it run to see if it stops.
And as Lynnmor says, if a simple plumbing fix is too much, an RV may be more than you can chew. At the very least, you must adopt a new way of thinking, completely different from your S&B house or a regular automobile. Imagine trying to take your house down the road. An RV has many many complex systems, all self contained, that must not only withstand camping in various locations/climes, but also must withstand constant tweaking, twisting, vibrations and bangs/bumps while traveling for miles and miles down often substandard roads. And most trailers have springs but no shocks, making that road abuse that much more intense on the unit. That translates into nearly constant maintenance and often repairs, much more often than a S&B house, and much more often than an automobile. Get used to it. Very seldom will you make a trip that NOTHING goes wrong.