AGM batteries are for rough service only, the conventional wisdom has warped them into something they are most definitely NOT. When I sold batteries in parts it became painfully evident they do not last as long as regular batteries if you let them sit unused for a while. Why like Optima will not give as long a warranty as a regular battery, they do not last as long. Deadly gas? It is as bad as a normal battery, which pretty much now recover most of that. I've seen an Optima run you out of the room when shorted to degas rapidly when charging.
I for one thought Optimas were highly overrated batteries, they certainly went defective fast enough.
You pretty much don't adjust charging voltage on anything since the old adjustable point type regulators went away.