Hi Bert the Welder,
I have AGM's because I got rather tired of laying down in the snow to check electrolyte levels in seven Group 29 12 volt jars, totaling 875 amp-hours.
There is only one Li formulation that can work at -40. It is still, as far as I am aware, not available in a 100 amp hour battery.
The other issue is HEAVY inverter use. AGM's are a bit better than Li at that. I often draw 190 amps from the battery bank.
My particular AGM's are telcom batteries that are 4 years old and were "reconditioned" pulls from Cell phone towers. They were purchased because of price. New, they would cost about the same as SiO2.
My next bank, unless I can find something better, will be SiO2 and that will probably happen in July or August 2021. I'm debating whether to get 600 amp-hours, or 400.
I have a lot of respect for Itinerant 1. He has done his research carefully.
I wanted my RV to behave as if it were plugged into shore power, without generator use. I mostly succeeded and for the first five years I did not own a generator.
I wish I had not caved in and gotten a generator. It has, since I started, cost me over $12000.00. Considering that I use the generator less than 100 hours per year, it is a pretty pricey item. For that, I could have had a rather large solar array with slide out "wings" and actuators to move them in and out.
If I had known in 2005 what I know now, I would have moved to a 48 volt battery bank.
Having a beer budget is quite a pain sometimes * grin *.
P.S. I have no relationship with *any* company that is selling anything.
SiO2 are not perfect. No battery is. But with a potential 16 year life span, and my recent change back to part time, they essential for me at age 72, have a life time guaranty. Their cost per cycle, lower initial cost, and the flat dead 620 times are icing on the -40 cake.