1*18650 vs. 2*18650 Battery Headlamp (Battery Drain Question)

I’m looking to buy a Q5 headlamp from Amazon soon. I found headlamps with a Q5 emitter, in one 18650 battery version, and two 18650 battery versions. Implying my 3000mah batteries are in working order, which style would give me more bang for my buck using?

What I’m asking is, would the two battery version give me the same effect as using a ONE 18650 battery version, but double the lifespan of battery, but without switching batteries out like I would have to with a one 18650 version?

I’m not that well versed in how these 1*18650 or 2*18650 Q5 headlamp drivers make use of the batteries to power the emitter. I’d like to have one of these 2 Q5 headlamps, one which I could get the longest use out of two 18650 batteries implying they are in good 3000mah working condition in this scenario.

Would I be better getting the ONE 18650 battery version, and then switching out the battery to a new one once its drained? or would the TWO 18650 battery version give me the exact effect of two 18650 (lifespan) without having to switch out halfway in between like I would have to with the ONE 18650 battery version?

You’ll probably get about twice the runtime in a serial setup, too, because it will probably have a buck driver then.