Might try looking in manual for a thermostat "reset" procedure. Not sure what year/model you have but if you don't have a manual, you can google the model number. You didn't say what battery you checked....but check/replace thermostat batteries.
Stan and Terri
Oak Harbor, WA
2008 Chevy 2500HD D/A
2007 Cruiser CF30SK
Glide Ride Pin Box
Reese 16K Slider
If the digital thermostat shows nothing, and there are not penlight (AAA) batteries under the cover, then the circuit is not getting power. Check the fuses on the converter, to make sure 12VDC is leaving the converter for all the circuits.
BTW, when you ask for help, you will get more specific answers if you tell people what make/model of camper you have.
Is your termostat a Dometic digital????? If so it should have a on/off button on the upper left side, looks like a circle with a line through it...Just saying...You know Dometic had a lot of defrctive thermostats, I know because I had one....
Rosie & Tommy
2017 Ford F350 Lariat Power Stoke DW
2013 Cruiser Patriot 305 SKP
In God We Trust
A proud member of the one percent...Semper Fi
Ours went out also. Try tapping the wall under the thermostat. We did that and the display showed for a little. We also called the thermostat mfg and they were very helpful. Dealer said bad thermostat- replaced under warranty.