Jagged is sponsored by varta batteries but not sure if they are lithium ion. I do know sappington did have a lithium ion battery sponsor at the mint last year. Not sure if he still has that sponsor.
Shorai batteries are also another brand I have looked at. But they say they require 13.1volts at idle haven't checked for sure but didn't thing a rzr magneto puts out that at idle.
I'm actually using lithium ion batteries for my vehicle and I find them great! We just have to be extra careful about them because there are severe safety issues with the present lithium-ion batteries that are used in electric and hybrid automobiles. However, a research firm says that it has found a way to make a better battery that can create a longer driving range by utilizing a solid electrolyte instead of a liquid one.