ThingFlings deal of the day is for 2 battery packs for the 360 with chargers
that can be charged via USB or plugged into the wall. I purchased one of
these from ebay a year or so ago and ordered this to use on my second
controller. The battery lasts pretty long without having to recharge and I
have seen any problems with it yet.
$1.99 + $6 shipping = 2 battery pack and 2 chargers
