I take it to mean the battery has got to be connected as directly as possible to the fridge because the battery is a necessary "shock absorber" for the electronics
for the compressor
refrigerators convert the 12 volts DC to a 3 phase AC at a somewhat higher voltage.
Mine converts it to about 22VAC 3 phase at a variable frequency depending on temperature and available battery voltage.
module (basically a variable frequency inverter) doesn't take a constant current
from the battery.
It takes a BIG bite and then actually RETURNS a bit of it BACK to the battery a fraction of a second later.
This happens somewhere around 40 times a second, although as I said, it varies with temp and battery voltage.
It's this event which causes noise in your stereo, VHF
etc, when the fridge is running.
It's also the reason you can't just run a fridge on a charger without a battery.
The charger won't take ANY current
in the opposite direction, and this refusal of back current might even damage the fridge's electronics.
That's why warnings are posted in installation documentation
A battery on the other hand, just thinks it's being alternately charged and discharged very quickly, which it actually IS.
A healthy battery will take this in stride, and an ocillloscope across its terminals will show a very small change in voltage peaks when this event is taking place.
A "Squishy" or weak battery could show noticeably larger changes, thus fooling the charger.
If the power leads for the fridge electronics go directly to the battery without taking the scenic route
through the panel, you have eliminated or at least reduced other possibilities for noise generation as well as reducing loss through long wire runs.
You need decent sized wire, and as short as practical.
Don't believe that just because the wire is original to the boat that it's good enough.
My boat had a #10 feed wire to my panel, and after adding a few things to the boat, I had to replace it with a #6, both + and - leads. WHAT A DIFFERENCE ! Fridge ran better, watermaker
had more output, etc.
That's just my opinion of course, but I've got many years of pro electronic servicing and yacht maintenance