^ I've purchased 2x12v with that in mind - what if one cell craps out - tho it hasn't happened yet. But being able to use just a single 12v has been handy to temporarily power up the camper during off season or it's inverter during a power outage or to carry around in the trunk when the car had a flaky alternator. And I might just retire one early to use for the home alarm or some other 12v device.
I've also purchased 2x12v because they were RV/Marine and thought that type would suit frequent heavy inverter use (not a consideration often mentioned). Plus somewhere I picked up the idea that as a corollary/consequence of the design ability for high rate discharge is the ability to accept a fast charge (something I wanted). But don't ask me for a link.
Last batteries purchased are 2x6v. They don't have an AH rating, only a couple reserve capacity listed but the size is similar to ~110 in a 12v. Gotta say tho, using my hopelessly old school metric of, "do they work" and "do they limit want I want to do", I'm happy them so far. We camped for 5 nights with them (a personal lifetime record by far) all without charging. Pass the Koolaid.
These are FLA btw. I'm gonna hate the off gassing if it corrodes the cabling, the one big dislike for me.
Venting is important. I'm not surprised FWC recommends AGMs, what with their interior placement and in a space with electrical devices. My batts are outside the living space and I don't be surprised if JaSAn's are also. In my world AGMs should be compartment vent anyway (
per Lifeline faqs) and not enclosed together with an inverter etc (
per GoPower eg manual), but it's a lonely world
AGMs are great. I went down the battery research rabbit hole years ago and came back out happy to pay for a premium brand, which I did. Next set were FLA. Reasons being, lower cost and "sufficient enough is good enough". Kinda the same mentality that put me into, and keeps me, in a FWC type camper as opposed to something "better".
Finally, a story about battery care... We had an electric stand up forklift at work. It had a large, tall, 24v(?) FLA battery bank. That machine worked hard and was charged hard, prob the charger was faulty. Usually, when someone actually checked, topping up the electrolyte took 1-2 gallons of distilled water, or more (!). That forklift was old when we got it and it may have had a new battery bank then, IDK, but it was used and abused it for another 21 yrs before replacing the pack. Who knows how long it could have lasted, had it been better cared for.
EDITED to add links