Do lithium flashlight and emergency light batteries count?
We do use lithium to store power at our cabin. A little more than a year now. GBS branded LiFeMnPo4 prismatic cells were the base for the system. It is a larger set than what one would use in a teardrop or a CT or most RV's, unless you were full timing in something the size of a bus. They are wonderful to have. Charge much quicker off the same solar panels. Light weight is not so important for our use other than it was much easier transporting and installing them than lead acid. I absolutely love not having to watch fluid levels as well as being able to shut everything down leaving the cells in a partial charge state with no worries at all. We only charge to about 90% so they may outlive me.
Not cheap, but we saved as we went together with two other families and bought a pallet of cells direct from China. Our BMS systems were designed and built by one of the others who is an electrical engineer.
The Iota IQ-LIFEPO plugin device seems a good deal, especially if you already have Iota chargers. I haven't used it except for an initial trial right after they were bought. If I had not already had Iota chargers I may not have bothered. The power used gets recharged quicker via the same solar panels, so there has seldom ever been a day when we actually needed to use the generator and Iota charger. That is also helped by the fact that the lithium can be left partially charged with no detrimental affects.
I still have a year at least on the GC2 batteries in the CT. I would very much like to use lithium when the time comes for new ones. I've looked at the Battle Born, and might go with them. Last time I looked Northern AZ Wind-Sun was selling them. I take that as a vote of confidence. Pricey. But I like the weight savings.
FWIW, I do not think lithium cells will get appreciably cheaper as more and more things are using lithium of one type or another.