Are you talking about running those cells in series? If so, you need a buck driver. Try looking at wight’s recent driver boards. If you’re going parallel, and you can wait a month, led4power is hoping to get the next batch of his 5A PWM-less drivers available by the end of January.
Edit: Oops, sorry for the misinformation. Wight’s recent drivers are zener-ready but not buck drivers. I was thinking about this one, I guess. But, it has bugs yet to be worked out. Sorry, I don’t know enough to recommend a good one. Maybe someone more knowledgeable will come along and help you.