Alcat,
Evan is right, it seems you are about right on for battery life with running the fridge.
If your car is taking 4 hours charging while driving I suspect an inadequate charge line wiring. We see this all the time. Likely there is not a properly sized ground wire coming out of the 7 pin on the car that is grounded to the chassis. Shops omit this ground wire a good deal of the time for some reason. Crawl under the car and look for a large white wire coming out of the 7 pin and screwed to the body or chassis somewhere nearby.
If you plug your dc voltmeter in and run the car, what does it read? This will often tell you the status of your charging circuit. I would want to see a minimum of 13.8v when running, nothing under 13.6v. Ideally it will be up over 14v if a large enough gauge charging line is used. It should charge up MUCH faster than what you are seeing.
Cary