Interstate is not a battery manufacturer, they are a battery marketer.
Who currently makes thge, if any ~125 AH AGM battery in their inventory, is anybody's guess and it will be whomever offered them the most profit margin( lowest bidder).
Batteries + sells X2 power batteries which are relabelled Northstar AGM, which are top quality in my opinion and experience. They are not an economical AGM. Northstar offers a 4 year free replacement warranty, batteries plus tacks on another year for 5.
But like All AGMS, they have some foibles. The Northstars really like high amp recharging, at least every so many deep cycles.
If you are not going to install solar right off the bat, this basically means that unless you plug into the grid, you will never fully recharge the battery, as the alternator, controlled by the vehicles voltage regulator, never allows high enough voltage for long enough, and even if it did get to 14.5 volts, and stayed there for a 5 hour drive, a battery at 50% charged when the engine was started, would still need another 1.5 hours of driving, minimum.
The alternator is not an instant magical battery charger as so many people the world over seem to think. It is capable of high amperage only when cold, with its voltage regulator seeking voltages in the mid to high 14's over thick copper circuit and with a depleted battery which can accept high amperage. a battery at ~80% charged starts limiting how much it can accept and by 95% charged can only accept an amp or 3 at most. As the battery ages it can accept less and less, even at higher voltages, which are rarely allowed by the voltage regulator anyway. So defniitely take advantage of this very capacble charging source, just know it is not all powerful and will rarely if ever actually full charge a deeply cycled battery, no matter how long the vehicle is driven. It sucks I know, but it is a fact and best to learn it before destroying a battery through ignorance, as so many people do, and then blame the battery for not being magical granter of wishes.
So without the solar, and without being to occassionally fully charge it by another method, like plugging into the grid overnight and letting a 12+ amp charger go until it drops to float voltage, then hold it there for many more hours...........
Then what quality battery you get is not much going to matter. The best AGM is not immune to chronic undercharging, so get a cheap one. Batteries plus has motre budget friendly AGMS, which are likely the same as this:
https://www.amazon.com/Universal-UB121000-45978-100AH-Cycle-Battery/dp/B00S1RT58C
Just with different labelling.
Also one shoud not really mix newer and older batteries together. The newer usually battery quickly degrades to the level of the older battery. Not saying it does not work, just that it is far from ideal to mix old and new, an the new will be short lived, no longer than the older.
125Ah in a AGM battery is kind of a rare beast, the Vmax tanks is one, the Lifeline GPL-31XT at a significantly higher pricepoint and quality level is another.
The group 31 Northstar/X2 power is only rated at 102AH, but would be able to power a 1200 watt inverter for significantly longer before the low voltage alarm starts crying. Even drawn down the same Amp hours from full as the higher capacity lifeline or Vmax tanks, would hold a higher voltage under a big load such as an inverter can present. Especially 1200 watts which is ~ 100 amps at 12vDC
Lifeline and Northstar can accept HUGE charging amperages when well depleted, the Vmaxtanks says to limit it to 30% of the 125Ah rating whic is 37.5 amps. Which a well wired alternator will be able to exceed on a depleted battery, for as long as the vehicles voltage regulator seeks 14.5ish volts and up to about 70% state of charge.
I don't really think exceeding that amperage is a problem, except if the battery is starting out at 100F or in that range. I am not recommending people dismiss the max amperage limits listed by manufacturers, but beware that the danger lies in excessive battery temperature. Do not dismiss the voltage limits however, especially in hot ambient temps.
I'd not expend big bucks on a top quality AGM until you can at least approach the 30% recharge rate and also be able to fully charge it regularly. Odyssey AGM says no less than 40% charge rate when depleted to 50% state of charge or less. They are similar construction to Northstar AGM
Full charge on an AGM is determined by amperage at absorption voltage. When holding the voltage at 14.4 to 14.7v, when the 100AH battery tapers to 0.5 amps of acceptance or less, it can be considered fully charged.
When most depleted, AGMS really like the higher amp charge rates, Fill this requirement and recharge to full regularly, and they will serve you well. Inability to meet these requirements and a flooded marine battery will likely outlastan AGM in the same usage for half the price.
Some peole assign super battery status to AGMS because of their price, but they often fail to live up to expectations unless treated very well, and this means a 20% charge rate minimum when depleted to the 50% range, and complete recharges no less frequent that 5 to 10 deep cycles( 50% range)
The less deep the cycle, the less important the high amperage recharge becomes. On my Northstar when I notice some performance loss, Lower voltages for same AH removed from it, I intentioally dain it to 50% or below and then feed it 40+ amps until it hits 14.7, then hold 14.7 until amps taper to 0.45amps or less(90Ah capacity). This is pretty much the capacity and performance reset procedure on this battery, and i am getting by far the best service I;ve ever gotten from any battery, from this Northstar AGM. It turns 4 years old in November, will likley have well over 700 deep cycles on it by then, many dozen to well below 50% state of charge.
For over two years now it has been my only battery, for both engine starting and house loads, and still easily starts my engine depleted 65 of its total 90AH capacity.
My house loads are a 1.8 cubic foot frodge, 90 watt (max, average is 32 to 35watts) laptop several hours each night, lights, fans, stereo, tv, and various other things. 200 watts of solar, wish I had 300, especially in winter when I need to plug in to achieve that high amp charge rate and the 100% state of charge.
