I would start by looking at $/AH and calculate how much longer another batty would have to last to break even and then decide if it's a worthwhile bet?
You said it much better than I could. Thank you.
AGM roughly 2X $ of FLA... only you can decide if convenience is worth the extra $. Properly cared for I wouldn't expect a large difference in longevity... poorly cared for you can kill both rather quickly.
I only know of three advantages to AGM. I may be wrong with these three and there may be others.
1) No need to water
2) Higher acceptance rate.
3) No positionally sensitive.
#2, if true, could be acceptable. I spoke to a tech at the battery manufacturer of my house bank AGMs. They recommended that their AGMs be charged at .2 of the C20 Ah rating. Lifeline goes even further and says that if their batteries should be charged at as high an amperage as practical, up to 5 times the C20 of the bank. They also say that if their batteries are regularly discharge to 50% or more of DOD than the charger should be able to charge at least at .2% of C20. I believe that the recommendation for wet cells is that bulk charging should be done at about 10% of C20 Ah.
For large banks this can make a difference. My bank was nominally 780Ah when new. Charging that at .2 C20 would be 156 amps. My charger is only rated for 125 amps (although I typically see 130amps during bulk charging). So I max out my charger. This means that I can get to the absorb phase of charging a lot faster than if I was limiting my charger to 10% of C20 or 78 amps.
The faster I can hit the absorb phase the better the chance that I can get my batteries fully recharged via my solar panel during the day. This might mean running my genset for an hour in the morning vs two hours in the morning.
As usual, I could be wrong but I think charge acceptance is potentially a bigger advantage of AGM for some of us than the maintenance.
