Superduty/karmabiker: The use of big gauge wire is all about voltage drop; if the distance from the battery to fridge is short like in my case, small, 12V, wire gauges work fine as the voltage drop is tiny however, if you are running a fridge in the back from a battery up in the engine compartment, then voltage drop is inevitable and big wire gauges mitigate this. These fridges have battery protection circuits, often adjustable (mine has three levels) so eventually the voltage will drop and the fridge will switch off.
U145505: Why are you running the fridge through the inverter and not using a 12V supply? Inverters are not as efficient and they typically have a dead load of around 15W or more from the battery even when not being used; mine has an on/off switch but some have a sleep mode that automatically detects that it's not being used and goes to sleep. This is a feature of more expensive inverters and it's unlikely you have it on your little 2000W one so it will be drawing power even when the fridge is on an off cycle. Where is your battery in relation to your fridge? Close or far apart? You are correct about your draw down rate; it's way too fast; my CFX75 DZW takes three days in fridge mode to draw down my 105Ah battery from 100 to 75% (highest battery protection setting) when used as a fridge. Do you have access to another deep cycle battery that you could borrow to make a test? Even new batteries can be duds.
