Glad to see that sort of stuff is coming along. I was thinking there must be something more cost effective than LiIon when you don't need to worry about the weight.
NiMH takes up more space than LiIon but costs less for the same amount of energy storage capacity. Toyota uses them in their hybrid cars primarily for cost reasons.
In Japan the technology that is installed is sodium-sulfur [1]
It operates at 350 celcius, is full of dangerous chemicals and require a certain size to be interesting, but under these conditions, it seems to beat other techs
