Regular Quark AA is what I would suggest. The bonus is that, if you want to expand your horizons, you can buy more bodies for it later:
AAx2
CR123 (single)
18650
You might decide to replace your Fenix lights with Quarks, as I did. Well, except for my TK30.
I actually still carry my Nitecore SmartPD D10 because of the great pocket clip and UI, but it isn't as durable as a Quark. If you're wanting a "deep carry" clip, you won't like the Quark.