I have some Samsung 25R on order, do those have the same counterfeiting issues? I guess I could still use the fake batteries I have since they do seem to work pretty well. Would just be interesting to compare them to actual authentic Sony VTC5's. Thanks again for your taking the time to give some excellent advice.
No, the Samsung 25R has no issues with counterfeiting, as far as I know. They are pretty inexpensive (you should pay no more than $7-8 each, and you can find them for less with a little effort), and thus don't have the same appeal (to counterfeiters) as the more expensive VTC5, which for a while were THE cell to buy, especially for the vape market.
They are also much easier to find from a variety of sources. Illumination Supply and Mountain Electronics would be my recommended source(s) for any type of lithium-ion cells. Unlike, say, Battery Junction, they don't sell crap *****Fire cells - any cell you can get from them should be quality. I have had only good experiences with IS and ME, and they know lights and cells inside out...if anyone can detect fakes and screen them out, it would be them. Craig from IS, and Richard from ME, also both are involved with CPF. Richard, for example, designed a custom driver for one of Vinh's modded lights, and Craig ran the CPF Christmas giveaway thread last year (2013, technically). Nothing like buying from fellow members of this community.
I think you are fine to use the VTC5, I did some looking, and could not find any mention of a safety issue. It seems the fakes are not actually too bad...just not as good as the real thing. And it is always possible you did get real ones, after all.