Hi, my name is XXXX. XXXXX are two things you need to do here. First would be to have that battery load tested. This can be done at any good automotive store. Remember they cannot load test a dead battery so make sure it has a charge before taking it to them. I'm sure you under stand I am not taking about a simple voltage test here I am talking about a load test. This sounds like your most likely problem.
Second, if the battery checks out ok then you need to find if there is a drain on the battery when it is sitting still. Here is a simple test you can do. Using a simple test light (pictures below) remove the ground cable from the battery, attach the alligator clip to the ground cable and stick the tester probe into the negative post of the battery. If you are getting a strong light then you have something draining the battery. You may see a small dim light and that is ok but a strong light is not. If this is happening you will need to find what is drawing power when the ignition is off.
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Thanks again
Tony
RV Mechanic
15 years specializing in all electrical problems, generators, inverters, converters, etc.