Just to clear up a couple of misconceptions between AGM and FLA batteries (not 6V vs 12V) - the difference between these two type of batteries is more than just that one vents and needs to have water added and the other doesn't. AGM has several other advantages over FLA:
- AGM can accept charge more quickly than FLA, which can be a significant issue if you rely on shorter periods of high current charging from you alternator to keep the camper battery charged. This is likely not an issue with a primarily solar charged system as the rate of charge is usually limited by the amount of solar power available.
Yes this is true - IF you can take advantage of it. My 200W of solar can't generate enough, my FLA batteries will take all the 110V 35A charger
will deliver, and unless you have big wires from alternator to battery you can't get a big charge from you alternator.
- AGM has a much lower self discharge rate and is less susceptible to sulfonation than FLA, which is important if you store your camper without solar or a maintenance charger. An AGM battery will likely go twice as long as an FLA before it needs to be topped back up.
It is true that AGM has a lower self discharge and will be an advantage if you store your batteries untended for long periods. Mine are stored on solar or a tender when not in use.
As to sulfating, I don't see how this could be true. The chemistry is the same:
Pb(s) + PbO[SIZE=11.199999809265137px]2[/SIZE](s) + 2H[SIZE=11.199999809265137px]2[/SIZE]SO[SIZE=11.199999809265137px]4[/SIZE](aq) → 2PbSO[SIZE=11.199999809265137px]4[/SIZE](s) + 2H[SIZE=11.199999809265137px]2[/SIZE]O(l)+ 2 electrons
the S2PbSO[SIZE=11.199999809265137px]4 [/SIZE]
collects on both positive and negative plates and the sulfur is returned to solution when charged (if you wait too long the lead sulfate hardens and is difficult to separate, which is one of the things equalizing does, which you can't do with most AGM batteries) .
- AGM batteries are often rated to 80% depth-of-discharge (DOD) at the same number of cycles as FLA will achieve at 50% DOD - meaning that you can get 60% more power out of an AGM battery than FLA battery and still have it last the same time. Or conversely you can use a smaller, lighter AGM battery to get the same usable capacity.
See graph from Trojan below: https://www.trojanbattery.com/pdf/AGM_Trojan_ProductLineSheet.pdf
Of course FLA is significantly cheaper and more widely available than AGM, and FLA works for many folks so there is no clear answer, just a bunch of factors to consider for your particular application.