Well I'm glad you got it figured out. 60% is definitely too low for any amount of boondocking. 6 years is about right for fairly heavy use, but with decent care. Or little use with not great care.
Just keep in your head that batteries like nothing better than a 100% SOC (State of Charge) and a constant float charge.
An occasional stir to keep stratification at bay is a bonus.
But if you're getting 6 years, a hundred bucks equates to about 17 bucks a year. And maybe 30 at full price. Big whoop. That's like one Starbucks a month. (Not a Starbucks guy, BTW. Just an analogy relatable to the common man.) Enjoy your life and have fun.
I have 3 of those batteries in my rig. They're probably about 4 years old and at 100%.
I've been wondering their Amp hour rating. I was figuring more like 100. Where did you see the 115 figure? And did it notate "20 hour rate" or anything like that?