It's simple
79w is about 0.7 amps at 120v but that is 7 amps at 12v
The killer is the compressor start up probably a surge of about 60 amps dc to provide 6 amps 120a.c. To start the compressor
That's why I have a 1200w inverter to run my 100w residential fridge
Compressor start is around 900w
Even if you got it started you would only get an hour or two of freezer run time
It's going to draw 7 amps from the battery while running
I doubt that battery is larger than 10 amp hrs
Your not the first one to miscalculat 120v power use to 12v power
You won't be the last one either
You might be able to return the battery station
Put that money toward buying a 600w inverter, that is 600w continuous 1000 surge, you need to be able to hold that 600w until the compressor spins up and is running, were taking one l or two seconds
Not milliseconds that most inverter surge ratings are
Connect that inverter to your RV batteries
That 500w connected to a small battery won't work
