New batteries, still not enough juice to run fridge over night?

The truck should still crank very well anything above 12 volts unless it's very cold. I think you're being sold a story. Batteries will drop to 12.7 soon after key off, and if there's any sort of load they will drop a bit more. Agm batteries do not behave a hell of a lot different than regular lead acid, they just last longer.

 

I put four new Optima yellow-tops in my fleet rig, and threw out the crappy cobra modified sine wave inverter, replacing it with a Go Power GP-SW1500-12 true sine wave model. Those two changes made all the difference. Now everything works great, and no low-voltage alarm beeping in the middle of the night. Everything from my laser printer, microwave, bunk heater, laptop, 120v air purifier... it all works very well.

 

I have the exact same situation in my 13 Cascadia. My current working theory is the alternator is not putting out 160 amps,. Try this,
When parking at night run the truck high idle for 30-60 minutes with everything off. Then see how long bunk heater refrigerator last.

 

Wouldn't him driving the truck all day be the exact same thing? If he just parked why would he high idle the truck?

 

I guess it depends on when you stop for the day. I usually stop at 11pm or so. My lights, A/C, power inverter having been on.

 

Get some odyssey batteries best battery you can buy they are ture deep cycle. 650 cc amps will out last any 950 battery. get that fridge update done