I have never had an issue with Batteries Plus in the over 15 years I've been using them.. I have had a couple of computer batteries they replaced....
They are not the cheapest source but you can find 'em most anywhere.
As for AGM batteries... 60 months (5 years) is a reasonable time to expect them to last. in fact it's a bit on the low end.
Flooded wet typically last 7-10 years
I've heard of ONE AGM hitting 12
But my experience with AGM's was not as good as "Advertised". in that they failed to outlast anything INCLUDING some batteries that were older than the motor home. I only recommend them where there are "Special Needs" considerations like "it is nearly impossible to access for maintenance"
Only time I've had an issue getting a battery warranted... That store no longer sells automotive batteries or does automotive service.