The VTC5 batteries we sell at my shop have the look of genuine VTC's, and most customers say they work like their older ones. So, either my boss has been selling fakes for a long time, or the customers have no clue what they're talking about (and both are equally possible).
From what I can see, they perform like they're supposed to. The one VTC5 I bought from my work acts like a typical 30 amp max battery should with my low resistance builds. After only a few rips with a coil that is pushing the battery beyond 30 amps, it gets hot FAST. So, whatever is under the wrapper, it definitely performs like a 30 amp. I used a VTC3 (or maybe a 4) once with a .12 build, and it definitely held its own like my MXJO/HE2. If that one was a fake - and I assume the possibility is high, because my friend doesn't check out his sellers as thoroughly as I do - it definitely performed like it should have. From what I could see, visually, it was legit.
I've read around on various forums, and it appears that people are saying most of the "VTC5" batteries are likely coming from laptop batteries, or some other source where the cells are yanked from, and are entering the market this way. If that is the case, then I would say the majority of these seemingly legit batteries are most likely genuine; however, they've just been re-purposed in a different way. Would I trust this NOS? Well, I guess that depends on where the cells are actually coming from, who was yanking them out, and the actual age of the cells.
For now, my one and only VTC5 is just sitting in a mech, with my Vapor Chaser, cranking out a whopping 8 amps. I'm a hair away from retiring it completely.