I'd recommend a 7.4v pack (Li-Ion or otherwise) for doing a LEDEngin setup where you (essentially) have "4" LEDs running. More specifically, I'd recommend 18650 cell types/sizes over 14500s. I won't go into WHY, but... it's somewhat important for the total "momentary" amp draw.

Whether you wire a LEDEngin in series or parallel (or a mixture... what I like to call "paraseries" or "seriallel", lol)... is up to you, and depends on your perspective/needs/project.