The 510 passthroughs are hit and miss. I have 3 right now. They all look the same but perform slightly differently(all acceptably though). I ordered 2 that I had to send back. One did not work outright, the other worked, but would fry the blue rechargable battery in about 10 minutes(literally fry, I mean hot as hell to the touch), I went through 2 batteries before I figured out what was going on(I initially thought the 1st battery was bad). I took that unit apart for sh*ts and giggles to see if I could find a short or something. It was all very cheap looking microcircuitry and bad soldering, also the board was labeled "Janty Kissbox" even though it was a generic Joye 510 passthrough(So the boards in the 510 passthru are the same as the boards in the Janty Kissbox). I have now ordered the 500 mAh battery's from batteryjunction.com for all my 510 passthroughs:
UltraFire 10440 AAA Li-Ion 3.6V Rechargeable Battery 500 mAh FLAT TOP CR10440 Lithium Ion
They seem to work a bit better and last longer(obviously 360 to 500 mAh) if unplugged.
My "guess" is that all the 1st run 510 passthru boards were initially designed by Joyetech specifically for the Janty Dura C passthru and/or Kissbox. Those that came in slightly under spec or "working but not quite to Janty's standard" were never assembled and labeled as such and sold to other smaller suppliers as generic 510 passthroughs. This may explain the unusually high failure rate in these particular initial generic models. However, since they became so popular, Joye has had several production runs since the initial run and quality has improved. I now see they are available in titanium and (I've got it on good authority) will be available soon in COPPER.