A bad alternator would be one likely cause, but that could include a loose or broken drive belt for the alternator.
If you measure the battery voltage with the engine running, it should be 13.6v or more if the alternator is putting out any charge at all. However, there is a mode of failure (diode failure) in which the alternator puts out standard voltage but very little charging current, maybe only 2-3 amps. Your coach will use more than that when driving, so the battery goes dead after awhile. You will need a professional alternator test to test for that problem. Most any auto parts store can do ti for you - usually free.
2004 American Tradition; 2014 Buick LaCRosse
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