I though Id chime in with some of my experiences Ive had with A123s in my featherweight.

I currently run 2 x 6cell packs in my featherweight (1 pack at a time) I dont run balancers in them, as I have found I do not need them. I balance the pack initially by matching the cells with voltages within 0.25v of each other. I then cycle them 3-5 times at 200mah. This is low enough that if one of the cells reaches peak before the others, it wont cook. After that it gets 2-3 charges @ 5amps, if any single cell gets hot compared to the others during this, I pull the pack apart (5min job with the http://www.modelelectronicscorp.com/...uct.php?pid=29