Franklinstein has it exactly right. From heavymetal's other posts, it's evident that he's not very experienced in the ways of hardware. Playing with lithium-ion battery packs is a dangerous way to start. NiCd or NiMH packs are much more forgiving, so that's where one might get initiated. The fact that heavymetal thinks that having seemingly identical connectors implies electrical compatibility is a sign that he is probably out of his depth, and therefore uncomfortably likely to get into serious trouble.
He should leave it alone. A lithium battery pack doesn't give much forewarning before going Ghostbusters bad, and we don't to lose Forum members to uncontrolled exothermics.
As Clint Eastwood's Dirty Harry famously said, "A man's got to know his limitations."