Your post brought back memories. I had a similar experience. I purchased a brand new trailer and started out on a trip to Alaska. About night three the battery was dead. I was still on the steep part of my learning curve about travel trailers and that caused some anxiety. It cost $173 (Canadian) for me to get an RV mechanic to run down the problem. A charging wire had been left disconnected during the manufacturing process of the trailer. A couple of years later I replaced the battery with a brand new battery. I two days later I had a dead battery. That time the charging system was fine it was the new battery that was defective. I now know quite a bit about trailer wiring.
I am not familiar with how your particular model trailer is set up. It may or may not be wired for the trailer battery to charge from the tow vehicle. You will need to find that out. If it is not it can be wired to do so.
Late model tow vehicles with factory trailer wiring harness will have a "hot post" in the plug that provides a charge from the vehicle's charging system to the trailer system. The tow vehicle owner's manual may even have a diagram that shows which one it is. If your vehicle does not have the trailer charging circuit it can be added.
That works pretty well if you are on a cross country trip and towing the trailer a few hours each day. Where you run into problems with that system is when you camp more than a day or two and don't run your vehicle or otherwise charge the trailer battery.
Don is correct, you need to make sure your trailer system is isolated or not drawing from your vehicle battery when you are parked and your vehicle is not running. Otherwise, overnight it can run your vehicle battery down and it won't start the next morning. More than one camper has fallen into that trap. I had 2003 and 2007 Ford trucks with factory trailer wiring that isolated the trailer system when I shut the truck off. However I had a new 2006 Chevrolet with a factory trailer wiring that did not. I had to unplug the trailer when I stopped for the night.
I wound up buying a high accuracy ac/dc multimeter:
I can now quickly and easily evaluate an entire electrical
system. It will measure voltage down to 1/10<sup>th</sup> volt and current to a fraction of an amp. I can quickly tell if a battery is charging and how many amps it is receiving. I can also measure amperage flow or current draw through individual wires. You can figure out just how much electricity each item on your electrical
system is producing or using. It will even test 1.4 volt watch batteries. I highly recommend that every FGRV member get one or one similar and also read up on RV and automotive electrical systems. It will save a lot of anxiety and cost.
The high accuracy at low volt and amp ac/dc instruments that will measure down to 1/10<sup>th</sup> volt or amp are hard to find in stores. You need to order from the internet.
I will attach a picture of mine testing the voltage of a 6 volt tractor battery.