As best as I can tell none of the available batteries have built in automatic balancing circuits.
Aero Lithium does offer built in connections for it's balancing charger at extra cost.
They recommend that the battery be balanced every few months with their optional charger.
You should read the presentation from Oshkosh on the Aero Lithium website.
I just replaced my almost dead battery with a new X2 lead acid because I want to wait for a short time before being an early adopter of this technology.
I have been trying to find the source/brand of the batteries offered by Legend and Flight Design with no success.
My intention is to replace my battery at annual in the spring with some brand of lithium iron.
I have no interest in any of the battery companies. I just want to start every time I turn the key.
Bill