A solid electrical system troubleshooting document

some model magteks have a relay that switches between battery power and converter power
also there is a main charging fuse and a main power fuse in the converter fuse panel

check the power at those fuses
and look for a battery disconnect switch, used while the RV is in storage to prevent battery drain
the switch is usually near the entry door
or
near the drivers seat 'console or overhead'
the switch controls a latching relay used to 'connect/disconnect' the house batteries