I guess I am questioning Grant's definition of "working perfectly". It could simply be that the fridge got
reasonably cold and the compressor eventually turned off. What we really want to know is the duty cycle.
How long is the compressor off and how long does it run for when it turns on again?
By way of example, at its "middle" thermostat setting, our Danfoss-powered fridge cycles On for 3 minutes
then Off for 7 minutes. This setting maintains the freezer at -6°C and the fridge at 4°C.
If Grant's fridge is running at, say, 15 minutes On/7 minutes Off, this would be symptomatic of it being low on gas.
Such a duty cycle would of course significantly increase the overall power consumption of the fridge and would explain the apparent shortage of House battery power.
PS. Questions for Grant. Does your fridge have an electric cooling fan? Is it still working as it should?
Has the cooling air supply to the fridge been obstructed in any way? (Just checking!)