What type of battery is this?

[Lera]

I am trying to determine what kind of battery my unit is:

Electronic Cigarette Batteries @ EC Transition

 

[Kent C]

I am trying to determine what kind of battery my unit is:

Electronic Cigarette Batteries @ EC Transition

There's two types of threads there. See the 'new' vs. the 'old' and while it appears to be a penstyle 801 type, I'd contact them directly to make sure before you buy.