In Summer its not an issue. But off season in Winter the AGMs most definitely DO need to be checked monthly and recharged as needed.
I had the same glorious thoughts about AGMs. Thus, I switched in my 4 boats, 2 tractors and RV. Guess what? After finding out that they were not cost effective I switched back.
My classic car had a Die Hard that was maintained monthly. I just threw it out just because. It was 23 years old and I couldn't believe it.
I get 8 years minimum out of a flooded battery in my boats and equipment. The key is water level and charge. The best I ever got out of an AGM was 8 years. That's what's not cost effective.