There is definitely something strange going on here that may have to do with the logic of the circuit. My ProVari worked fine, then the window popped and it was sent in for replacement. I only use 18650's with the extension, both the high drain 1600 mah's and the Trustfire 3000 mAh's.
I have no idea if i got the same unit back or ProVape did sent me another, but my feeling is that they sent me another unit since I have a completely new behavior.
1) As with all of you, I have noticed an extremely short battery duration with the second unit. With the first unit, the batteries would take at least 8 hours to charge. With the second, they were charged within an hour or two. That told me that the battery was not completely drained when I put it in the charger. Next time around, I compared the reading from a voltmeter to the Provari and the Provari showed about .3 volts less than read on the meter. The PV also put out less voltage than the meter indicated. I sent it back and received a new one. The same thing happened with the replacement.
2) I started frying SR attys (Joyetech 510) at a horrendous rate, and I was vaping at only 4.3 v. That is not high. Sent the unit back AGAIN, but same problem.
3) After frying my 4th within less than a week, I switched to HR attys and upped the voltage to 4.9.
Guess what!!! Battery life improved dramatically-now back up to the +1 day of heavy vaping and no more fried attys-at least for the time being.
I will give this a few more days.
ProVape definitely changed something in the circuit to pump out a lot more voltage with standard resistance attys between my first unit and this, which is now my fourth.
The service has been quick, admittedly, but I have already lost $18 in Postage and $20 in attys and am not prepared to put up with more costs.
I may be cutting my own throat on this since these types of posting do impact the resale, but I am in this to stay away from cigarettes and not for the joy of vaping.