Similar issue here. New Camper - Only some 12V power on Battery?
120v connected, everything works.
12v only, the electric lift works and I have seen a red light on in the fuse box - so it gets juice.
I replaced the blown 30amp fuse in the fuse box. Checked all other ones the fuse box.
I checked the inline fuse from the battery, near the battery compartment. Also checked the green (ground?) encasement fuse.
What am I missing? What else could it be?