To answer your question, your coach batteries are charged by a converter, that turns 120VAC into 12VDC and then sends it to your coach battery. If you are not getting at least 13VDC at the coach battery while on shore power, then you will need to check the AC breakers; you should have one for the converter, cycle that breaker, if it is 'on', and then test again. If still no go, then find the converter (mine was in the same compartment as the shore power cable, but yours is likely different) and check for a fuse or a breaker on the device itself. If you are comfortable with electrical stuff, then you can grab a meter and check for AC input to the converter, and then check for DC power out. It's possible your converter is bad.
2006 Damon Daybreak 3276 35'with 5 Star Tuner. 3 200 Amp Lithium batteries and 2000 watt PSW inverter/charger. 2013 Elantra on a Master Tow dolly.