Before spend money on an RV tech take a moment and do some basic investigation. Check your fuses and breakers, the dim lights when plugged in are a dead giveaway that the battery is not getting charged and the battery was powering the lights. Either a breaker is tripped, a fuse is blown, or the converter/charger is dead. Below I put some basic troubleshooting steps in order of difficulty from easiest to hardest.
RESET ALL THE BREAKERS:
With the shore power cord unplugged go into your coach and turn off every circuit breaker. Make sure they are all off. If one of the breakers only looks mostly off push it firmly to the off position. Then turn all the breakers back on
CHECK THE FUSES:
The easiest way to check a fuse is to unplug it and look at it. You should see a bridge between the two blades of the fuse. If the bridge is broken or missing, the fuse is blown and needs to be replaced. While it is entirely possible for the fuse to be blown and the bridge still looking intact, that scenario is pretty rare.
LOOK AT THE LIGHTS:
This step is easier with a helper but can be done alone. With the shore power still unplugged go into the RV and turn on a light and judge the brightness. Now while still looking at the light have your helper plug in the shore power cord. If the light gets brighter your converter/charger is probably working. If there is no change with the power plugged in then the converter charger is probably bad.
TAKE A PICTURE OF THE BATTERY AND GET IT TESTED:
Use your phone and take a picture of your battery while it's still hooked up so you know where all the wires go. Then charge the battery up and take it in to an auto parts store to be tested. If you would rather not pull the battery just skip the previous sentence, but still take a picture of the battery and the wires hooked to it.
BUY A METER:
Buy a digital multimeter from Walmart,Canadian Tire, Harbor Freight, or any auto parts store. A cheap meter should be $20 or less and every RV'r should have one. Open up the package and ask the counter person to show you how to check the voltage of one of the batteries on the rack. You should see somewhere in the 12.x volt range. Now take your battery (or a new battery) home and hook it back up. (You could also has a friendly neighbor to show you how to use the meter)
CHECK WITH METER:
Use your meter to take a voltage reading on the battery and write that number down. Now plug the shore power back in and take another voltage reading. If your converter/charger is working the plugged in reading should be around 13.6 volts or higher. If the reading is unchanged when plugged in then your converter/charger is suspect.
CONCLUSION:
You mentioned early on that you have very limited knowledge so I tried to keep this fairly basic. If at this point you believe your converter/charger is bad then it's probably time to call the rv tech. But at least you will know that you did some basic troubleshooting before laying out your hard earned money.
OTHER THOUGHTS:
Your tests at home support a converter/charger problem. The lights and refrigerator (even on propane)are battery powered, the microwave is shore powered.
Your friend probably did not affect your trailer when moved with his tractor. An RV refrigerator running on propane will only make it about a week on battery power. Sure the LED's on didn't help, but the refrigerator and lp detector are really what killed the battery.
The 15 amp plugged in at the campground did not cause this. It really sounds like your converter/charger is dead which is why the battery is not charging when plugged in at home.
Good luck with your trailer and let us know the ultimate outcome when you get it resolved.
