I have 2 of these PVs. One black battery and one silver battery. I have noticed that when I use the black one I get a really hard, almost harsh, TH. When I use the silver one, I get a great, but smooth TH. This is with the exact same carto too. Anybody else experience anything like this. I get a hard TH with the black one, but less vapor. I get tons of vapor with the silver one, but a much smoother TH. Does it mean the black one is faulty? Anyone...?