The 2016 Zion uses the Northstar AGM400, which is an excellent battery. Peter Lange at RT, just before he retired, was pretty frank with me about the problem: Even with the Northstar battery, the capacity is not enough. He suggested adding batteries. I have since been able to add 2 Lifeline AGM's to bring it up another 200AH. This was a somewhat complicated installation to accomplish safely and securely in the only 2 remaining under-carriage open areas. Alas, this improvement turned out to be barely enough for a couple of days of disconnected boondocking with modest sun on the solar panel. We have decided to add another Northstar AGM400, which will have to go topside, as there is no more room underside. This will bring the total capacity to over 1000AH, and I think this will "solve" the problem. Before he departed for his retirement, Peter also said that, running below 12.0V risks damaging the battery. The hard news is that ya gotta get more AH...a LOT more, to make the Zion work right -- unless you want to be awakened (or have your camping neighbors) awakened at all hours of the night with the Volt-Start cranking up the engine (then having no good way to "up" the idle so that it really puts some power back into the battery). And, it turns out, that we will be able to ramp up to 1000+AH for less than the cost of buying and installing the obnoxious Volt-Start. But remember, I'm skilled, and can do a professional and responsible job of it without paying zillions to some inexperienced and under-skilled mechanic at the RV shop!
Redroadtrek posted while I was writing this, so some of it doesn't apply now.
The Northstar AGM400 is not a 400 amp hour battery, it is 182 amp hours, so you have 382ah currently and if you are only going to 50% (more on that later) that is 191ah. Add to that if you are short charging, which is highly likely, you will only get to about 80% full (it takes up to 10 hours to get totally full), so you have only 30% usable capacity from your existing batteries, or 115ah, which is about what it will take, with a little sun, to run two days.
Love Peter to death, but more current information (which is available on this site), is indicating that going below 50% state of charge on AGM batteries, or wet cells even, is not the death threat we all have been led to believe. In reality, going from 50% down, to 80% down will only shorten the life of the battery by about 10%, if you use the total amp hours in and out which is what counts. The charts show number of cycles, which doesn't make for a decent comparison as you recharge less often if you go deeper. In your case, with the likely short charging, you would double your battery capacity by going to 20% instead of 50%, which would give you more like 4 days off grid. I will get links on here in a bit so you can see the logic behind going deeper, with the data we have found. This is a controversial issue to many people, but the data is really pretty clear, at least to some of us
IMO, you may be shortening battery life quite a bit by the mix of battery chemistries, manufacturers, and capacities. I think I would get some voltmeters on the them to see if they are evenly charging and discharging. The short charging, if you have it, will make this issue worse also.
If you have short charging, which will shorten battery life substantially if not addressed, you need to get a completely full charge every 7-10 charge cycles. The best way to determine the full charge is with a battery monitor that checks the final amps and volts to determine true 100%. If you don't get full regularly, the capacity will walk down over time.
In summary, you now have 382ah capacity, or which you are likely only using 115ah. You can instantly double that usable capacity by going to 20% state of charge, and will incur only a tiny penalty in battery life, which is likely less penalty than you are getting from short charging and mixed batteries. If you do add another AGM400 you would have 564ah of capacity (not 1000ah) of which you get 169ah usable at 50% discharge, and 338 ah at 20% state of charge limit. That would be 3 times the capacity you are getting now, I think. Of course, you will be hauling around near 400# of batteries and using up a lot of space with them.
We have a very similar setup, and likely similar usage. 440ah of Lifeline batteries, 300 watts solar, compressor frig. Normal use of 30-60ah per day depending on conditions. With no sun, we can go about 5 days if we are full when we start, closer to 3 days if only at 80% from a short charge. If we have decent sun we can go forever off grid. All of our charging is set up to allow us to get totally to 100% charged, if we have the time to do it, and we make sure we get there about every 7 charge cycles. 382ah of battery capacity is very large compared to what most people have, and should let you stay off grid at least 4 days, and more based on solar output.
Personally, if I were in your current position, I would get some monitoring on the mixed batteries to see if they are playing well together, and then start going to 20% state of charge instead of 50% (assuming you can accurately measure the state of charge with a good battery monitor, which can be tough with batteries in various locations, voltage only is not a good indicator of state of charge) and see how it goes for you. I would also confirm how full you are getting after various charge cycles to determine if you are actually short charging most of the time and if you ever do get totally to 100%, which also requires a properly set up battery monitor.
IMO, you shouldn't really need the Voltstart, as you have enough capacity to cover usage for long periods. This give you the option of manually starting the engine at convenient, and non intrusive to other campers, times. Even at idle, you should be able to recover one day's use in about 30 minutes, and if driving about 20 minutes which is about what it takes to go the dump station or trailhead, many of us have found.
