This is the product for 4s, 6s autocharger also exists - http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=73942
I was thinking of using two of these to charge two 4s batteries at the same time - my interest is in the lack of buttons or settings I would have to bother double checking, an overall smoother experience. I think these would be more enjoyable to bring out on the go - even better for compactness if I can repackage them with their power supply into a single package. At the moment I am using an accucel charger with a power brick that has long cables - useful for the home where wall plugs are in all sorts of weird places but for travel I much prefer something a bit less unwieldy.
Thoughts?