1st time trailer owner, question regarding battery/power

Sorry just at work at the moment.
The battery is still connected. For a brief moment, when i went to the bathroom which has the battery/water guages, it lit for a matter of a second.
There is no AC in the unit.
Plugged in, the only thing that works is the microwave. Fridge does not (havent tried using gas on it), no lights, no stereo, no fan. I turned on the red switch by the sink, i assume thats for the hot water tank?? and it did nothing as well.