"Vamo" more like a
style of battery device, since it is made by different manufacturers. If you search for pictures of the Vamo, you can find some with colored plastic buttons and other differences, but those are mostly older versions.
In looking through pictures there appears to be more than one body design for the V3.
#1 seems to be the most common. It has 2 extension tubes of the same size. Mostly likely 1 is for an 18350 and with both an 18650 would fit.
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#2 - But then there's this strange creature. The extension tubes are two different sizes. It doesn't look like they would be used together. It appears that the shorter one would be used for an 18350 and the longer one (by itself) for an 18650.
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I could be completely off base about this being your issue, but when I saw the 2 different designs it occurred to me that if you had the second one, putting the 2 tubes together (which seems logical) would make it much too long for an 18650.
Anyway, I figured it was worth a shot. Good luck.