Lithium Ion vs Lead Acid

I wonder if there are any battery technologies that look promising. Supercaps charge fast, but don't have that much energy capacity. I've seen others, but they require the battery to be at a very high temperature.

Of course, there are flywheels, but those are not exactly vehicle friendly. Maybe Velkess's design, but they have been quiet after their kickstarter was funded.

I'm sure there is a usable battery technology that is RV friendly out there. Oh well... I'm not looking forward to buying AGMs, but it seems that for this application, it seems to be the best way of doing things.