fwiw....
i'm building a few superbaddass battery system out of toshiba laptop parts. the finished product is flat, small (a little larger than the wally batts, but way thinner), outputs about 11v and its 5600mAh.
these are not the jamie lutch models. different parts that I just happened to pick up a wholesale lot of. they will be solid.! I'm pumped to build one for myself. the flat pack makes for easy packing in the gear bag. Pictures pending....
fwiw, these will be perfect for the 671s.