Searching through GearBest on their offerings they don't show which battery to use on the majority of their numerous 303 listings, but a few do. One says 2 X 18650, another says "3.6 VDC battery" and another a single 18650..... My bet is they are designed to use a single 18650 and the one listing which shows 2 X 18650 batteries is in error.
I have a pointer much like this with what I believe is the same diode and driver, it works the same using a single 18650, two 3 VDC lithiums or two 18350 4.2 VDC batteries @8.4 VDC total, although I'm probably pushing it with that much voltage. I believe it is designed for a single 18650 at 4.2 VDC fully charged and the driver is set to produce the same amount of current to the diode regardless of the input voltage, that is what they are designed to do to keep from over driving the diode and killing it. I measured the output power on mine using a LPM and found the output power does not change with any combination of the above mentioned batteries, as long as I give it 3.7 VDC, probably even a bit lower.
All in all from what I can find, my recommendation is to use a single 18650 if that is the right physical size, which I believe it is. I don't blame him for asking, there is too much conflicting information on Gearbest alone. Someone told him he posted his first post on this question in the wrong section, so he took their advice and posted here. That said, we have at least one individual who keeps coming to the forum under numerous new names, often a fishy name, if you get my drift, and tries to rile members by posting in the wrong section or asking questions they might be able to google just as easily etc., in general just trying to provoke members to respond negatively. The troll he has become was upset when banned and because of being unable to reconcile the issue within himself, is now seeking to upset others, poor dude is still mad at the forum. Doesn't mean this particular guy isn't legit though, fishy or not, so I answered.