Get the sub-c packs. Sanyo, GP, Intellect (I made my own...ugly as sin but it works well).
If you get the 4/5A-2/3A-AA whatever cells...they'll rattle around in your CA Crane stock and bug the crap out of you.
Those "A" cell packs are meant for the KA/G&P crane/mod/clubfoot stocks that are slimmer.
Go easy on closing your stock...with SubC cells it's a tight fit and there's not a lot of room in most stock tubes with the retaining screw in place. Lots of guys slice through their wires because they aren't careful.
Consider a "LiPo" stock tube...they're thinner walled (but still pretty stiff) and the retaining screw/plate is set really far down the pipe. The extra room will be handy for the battery cells and wiring when you collapse your stock.
Or...just don't collapse your stock...