I've been vaping on two sets of UltraFire CR2's for 3 months now. I think their capacity is starting to fade a bit, but they still work fine. I have another two sets I got about a month and a half ago, UltraFire also, and no problems with them either.
On capacity, I get about 2 hours of heavy vaping on a set of CR2's. So they aren't great, but overall no issues with the UltraFire batteries.
What type of charger are you using?