safe battery is dead !

1.) If you have any charge left on the battery, you can try the factory setting master code.  The sequence is: Enter-210104-Enter.  If you are lucky, the message will say "DELAY" and then will open after 10 seconds.  I was not lucky here.  My lock cylinder wouldn't move, so I would receive "ERROR2".

2.) I contacted several units within Dometic (marine, hospitality, etc).  None were able to assist me.

3.) The manual mentions an "emergency" key.  I was able to scour the internet for the small tool that spins out the black plastic cover to reveal a key receptacle similar to one on a bicycle U-lock.  Unfortunately, the keys are not the correct ones and Dometic doesn't sell them. You seem quite creative, so perhaps you could try 3D printing your own key if you're willing to spend some time.

4.) I gave up and learned how to drill a safe.  I drilled through the front, put a screwdriver through the hole and levered the small latch.  Okay, maybe I had to do 2 holes because I didn't know where the release would be!  I then bought a magnet to cover the hole.  Yes, the safe is ruined, but I got inside.

Once open, I can't see how it is mounted to the cabinet.  I wonder if it is mounted on a panel underneath and the panel is permanently adhered to the cabinet.  It was frustrating.

For others who might want to see, you can check the voltage on the batteries by: Enter-8-8-Enter.  If you see 6,0 - 4,9 you are charged.  If you are 4,8 - 4,5 you should replace batteries soon.  If you are 4,4 or less, batteries must be replaced (inside the unit).  The manual says batteries last one year.  "Bat-lo" is also an indication that you need to replace them immediately.