Liberty Coach has been using Lithium batteries for awhile as house batteries. At the Prevost Stuff show in Tampa I talked for awhile with the folks from Volta. The make a configurable Lithium Battery system for RV's that is stable. You just plug in the the number of battery cells you need for the job. The founder as I recall came from Johnson Controls. They also make and sell a 48 volt alternator for charging the batteries and a DC/DC converter for converting the 48V to other system voltages.
I was very impressed with the power density of their systems. I understand the pricing is prohibitive for all but a few applications. If the pricing came down I would love to give it a try.