Any of the IMR rated batteries will get the job done choose a flat top so it fits without forcing the cover closed I personally use the efest 18650 2500 mAh batter at 35A but do also use my VTC4 and VTC5s in it as well. just make sure its IMR rating and your good to go. I do have a set of IMR 18350's for it as well but haven't needed to go above 4.5 volts for anything yet.