AGM batteries aren't really a good fit for the typical charging pattern a vehicle will see.

I work in an industrial/commercial back up power company and we use AGM's built to our specifications exclusively. Our charging scheme is optimized for AGM's, a vehicle's isn't. We specify a room temperature of 77 degrees, with hotter cutting life expectancy, I forget the percentage loss of life per degree above 77, but it's not minimal, no way a vehicle's AGM battery can be maintained at that temperature. We test them regularly, just got back from testing 160 of them at a local 911 center.

We only warranty the batteries for 3 years and recommend replacement at 5. Of course most of the customers I deal with will have substantially more severe issues than a tow home if their backup fails.

So as said, don't waste your money.