If your comparing a 120 D4D with a 150D4D there is no difference.
If you are able to run your fridge for two weeks off the batteries you are doing nothing wrong. You are a legend!
120Watts is 120Watts! At 12 volts this would equate to a circuit current of 10A. At 220V the current
in the circuit would be .545A
It is better to run the fridge from 12V as the inverter and the 240V power supply in the fridge
are not 100% efficient. Therefore battery power is wasted stepping the voltage up then down
The problem with the factory outlets is they use thin gauge wire. This results in a voltage drop and
loss of efficency. The current Instead of running your fridge is wasted as heat in the wiring loom.
The bottom line though is, if your current system works well for you don't change it!