Running dual inverters, with one dedicated to the freezer?

Deep is below 12.2 volts.
Cold is below 32 degrees outside temp. Your battery box isn't heated.
Deep cycle 12 volt flooded batteries don't exist. No matter what the sticker says.

 

As far as I read it correctly in search "An AGM battery in your RV or boat will crank faster in colder temperatures than a standard battery. Because AGM batteries have a low self-discharge, they stand up to cold temperatures. AGM batteries can also be stored for longer periods of time before a charge is needed than the average battery"
So, basically any cold weather AGM concerns are moot?

 

gg, what I was saying, I don't have to run batteries deep in cold weather, cuz I'm running the engine

 

Flooded deep cycle batteries have been used for years in boats. Mainly because they’re supposed to discharge slower, and are able to be recharged more often. The discharge rate is labeled as amp hrs. Starting amps are rated as Cold cranking amps. Our boat had a deep cycle. It was good for leaving the lights on or playing a radio when night fishing, still having enough cranking amps to start the engine, and charging the battery back up. Constant draining and recharging a cranking ( starting ) battery shortens it’s life. Battery technology has improved a lot. They now have combination batteries that are supposed to have both characteristics. Ideally isolated deep cycle batteries for accessories and a starting battery for starting. Or probably more likely an isolated Starter battery, to insure the Truck always starts. My Dads Company Freightliner had that in 1995. It’s done with an automatic solenoid. Before that, his Trucks always needed a jump start after about a week. That’s all I know. AGM batteries are out of the question for Me. Too expensive. Dealerships always have 900-1000CCA batteries for $120 or less. They always last Me at least 3 yrs. I’ve always ran only 3 batteries. When it’s below 0, after a week, I often need to jump start. 4 batteries is suggested in below 0. I’ve never had an inverter till now. I’m sure 3 batteries isn’t enough. They’ll surely last less, though I start the Truck when making coffee, the fridge stays on always. Lately I’ve noticed it discharging while making coffee. I may already have a problem. I just don’t want to burn up another inverter. Lol

 

If you are wired correctly you won't burn up an inverter, any decent quality one has low voltage protection/cutoff and you'll get some audible beeps before that. I hear mine all the time, have for years, but only when it's about time for batteries.

I'm still considering AGM because I don't run where it's very cold and also I'm home every weekend and when the truck is parked it's plugged in. My inverter has 3 stage battery charging built in so it's on float all weekend/off time.

Getting over the price hurdle is the hard part. I have 4 group 31's

 

Do not connect different battery types together without an isolator (typically a contactor - a very high-current relay). You will kill your starting batteries very rapidly if you do not have a low voltage disconnect circuit that opens the contactor once you start draining the batteries. Starting batteries do not survive deep discharge very well, which is why deep cycle batteries exist, and deep cycle batteries do not put out huge bursts of current, which is why starting batteries exist.

With regards to the original question, the main issue is the internal resistance of the battery bank. Lead acid batteries of any type can only supply a certain amount of current for a period of time. Deep cycle batteries, which are the ideal type for inverters, have a higher internal resistance than starting batteries. The draw of both inverters may exceed the capabilities of the battery bank. Battery chemistries exist that can discharge tremendous amounts of current (for example, LiFePO4, Li-titanate, etc.) but still have decent safety characteristics. However, they do not tolerate winter weather so well (LiFePO4, for example, can't charge below freezing without potentially fatal cell damage).

https://www.itacanet.org/eng/elec/battery/battery.pdf