DC will not work

Sounds like you aren't getting power from the battery to the 12V electrical distribution system. There are a good many possibilities, but a little bit of sleuthing should be able to get it figured out.

Check the ground at the battery first. Assuming it's good, it's time to start tracing the wire(s) from the battery. One connection will go pretty much straight to the breakaway switch for the brakes (assuming you have electric brakes). One connection should go to the main house circuits, probably with a large fuse or circuit breaker near the battery and a disconnect switch somwhere in between. There may be a couple of other leads as well for various things (inverter, always-on LP and/or CO detector, etc.). Also, in general, make sure the battery connections are made to the correct battery terminals; sometimes it's easy to get them confused when changing a battery, and some makers don't go out of their way at all to make things consistent or predictable regarding wire colors etc.

If you can figure out the wire to the panel, see where the connection is breaking down. The main fuse or the disconnect switch would be my first guesses, assuming the connections around the battery are all good.

If you get stuck, posting a few pictures here would likely be helpful to those of us attempting to lend aid.

The battery. Disconnect switch fuse at the battery