Built in fridge help please

When I park up fridge turns it self off after about 4hours I can hear what sounds like a compressor trying to start but refuses to start fridge until engine started the fridge starts running no problem at all then until I park up again anyone any idears thanks

Faulty batteries? May have a cut off if voltage drops too low.

Conan beat me to it.

99.9% as above
Normal fridge / freezer operation it should run a max 24 hours if the ignition has been turned off this allows for weekend draining of batteries and also if the fridge is not opened it should stay relatively cool after that for a while.
Get your batteries checked…
Just to clarify the weekend drainage. The fridge should run for 24 hrs then shut down if the ignition ie truck is not started this should prevent flat batteries …

Cheers I’ll get them checked ASAP