Interstate is a battery marketer, not a battery manufacturer, and the places which sell interstate batteries can portray themselves as battery guru's, but in fact they might be overwhelmingly ignorant and or dishonest, as they want to get the current stock off their shelves, not get you the best battery for your application.
That said, there is only ONE 12v wet/flooded battery which Interstate might market, that can be considered deep cycle, and that is:
https://www.interstatebatteries.com/prod...12-hcl-utl
It is likely manufactured by USbattery, as are their GC-2 6v golf cart batteries.
Now will the GC-12 last as long as the GC-2 depth of dicharge and recharge regiment being equal. i cannot say for sure, but I suspect not. But the GC12 will last significantly longer than a marine/dual purpose 12v battery in deep cycle duty all factors being equal.
So comparing the gc-12 ro GC-2, a pair of gc-2s for 12v will be about 220AH of capacity, a single GC-12 will have 150Ah of capacity.
AH per $, the GC-2 will likely be the best deal, and likely last longer in deep cycle duty, all factors being equal.
https://www.battsys.com/us-battery-us12v...12-battery
https://www.interstatebatteries.com/prod...c2-ecl-utl
But Does one really need 220Ah of capacity? if one only requires 150Ah of capacity then one GC-12 will be cheaper than two gc-2.
Then there is the philosophy of how much capacity to carry. Some people get a lot of warm and fuzzies from lots of battery capacity. The problem with this is if that larger amount of capacity is consumed, then larger amounts of solar or charging sources will be required to fully charge them. In theory the lesser % amount of discharge of more battery capacity should equate to more total cycles and a longer total life of the batteries, but that assumes that they are indeed getting fully recharged before the next discharge cycle begins, and fully recharging a larger capacity of batteries is more difficult, requiring more solar and or other charging sources applied in the morning.
A lesser amount of capacity does not give as much safety margin, but lesser amounts of solar wattage stand a better chance of being able to fully charge the battery by day's end, and reaching full charge before the next discharge begins, is excellent practice, but not always achieveable.
The other factor is weight. Two gc-2s will be about 130 Lbs and take up more space than a single gc12 at about 82 Lbs. 50 Lbs does make a difference in Mpg's, especially crossing mountain ranges, especially in a smaller Van/vehicle.
Now my personal philosophy regarding capacity, has changed dramatically since I first got solar. I used to have 345 Ah total capacity including the engine battery, and 130 watts of solar. I was rarely getting more than 2 years from those marine group 27's cycling 2 of them( 230AH). When I switch from 2 g27s to one g31 as my house bank, I got 3 years, carrying less weight and spending 130 vs 230$. So in my case lesser capacity lasted longer for less money.
When that group 31 wore out, I was down to my g27 AGM battery which had primaraly been use for engine starting duty/ house battery backup, and saw that i could use that battery exclusively for both engine starting and house battery duty.
So I basically went from 345 total Ah capacity, to 90Ah total. 170Lbs of battery to 74Lbs, This northstar AGM battery turned 5 years old last November and has over 1000 Deep cycles on it. granted it was a 350$ battery and i could not keep ti happy via solar alone as it has high amp recharge requirements that solar cannot meet.
Personally, in an Astro/safari I would carry one single GC-12, with as much solar as one could stuff on the roof, and do my best to not need to suck more than 75AH from it nightly.
The 50% rule is kind of BS too. Reading the internet one might think that if they take the Lead Acid battery below 50% charged they are instantly and irretreivably reducing the capacity of the battery. This is noot really true. One can take the battery lower, as loong as they can recharge it fully before the next discharge cycle begins. Discharging it below 50% simply makes it more difficult to fully charge it, especially via solar alone, before the next discharge cycle begins.
I have hundreds of deep cycles on my current agm battery to well below 50%, and I took it there knowinng I could tthe next day, plug in to reach a true full charge with high initial amperage and a solar all day thereafter thing, or high alternator morning amperage followed by solar.
There is No one right answer as to how much battery capacity to carry. My personal opinion learned/modified over the last 12 years since I first got solar, is to not carry huge amounts of capacity, as it gives false warm and fuzzies. My warm and fuzzies now come from excess charging ability with voltage optimized charging sources. I have 200 watts of solar on my roof for 90Ah of AGM battery, and a 100 watt portable panel I can break out. I'd much rather have more solar than more battery capacity, but I also rarely require more than 60AH of capcaity overnight.
Less battery capacity means less weight to bring upto speed and slow down, and as RVs are usually overloaded, I'll gladly carry less weight in lead.
When i had a group31 USbattery as my house bank, I found out that it required high absorption voltages (14.9v) held for longer, than expected( pretty much all afternoon) , to reach full charge. Healthy gc-2s do not require this extended absorption voltage duration, meaninng they are easier to fully recharge. If I did not spend a lot of time experimenting, using a hydrometer, i would never have gotten 3 years out of that 12v group 31 marine battery. Will the 150Ah GC-12 be as stubborn in regards to getting that last few % of charge into, I cannot say, as I have not cycled one. i do suspect it will be quicker to get to a true full charge, but no actual data.
The GC-12 size group is also available in AGM. The Trojan t-1275 is a gc-12 size group, and I would much rather have one of those than a US battery/ interstate branded gc-12
I AM CRAZY ![[-]](https://vandwellerforum.com/images/collapse.png)
Oh yeah I almost forgot the most important part,,,, If Queenie lays on the panels,,,you'll need more of them. 
Now Q & I are gonna have a lie down.........Our heads they are a spinning 
