Also, I'm not sure I'd recommend lower voltage cells. If you're worried about blowing up, make sure you get protected lithium ion batteries or you could go with LiMN batteries that are chemically safe. If my internet search-fu is right, A123 batteries have a 3.6V charge voltage and a nominal voltage somewhere around 2.8-3v. You'll have a better vaping experience with batteries that have a nominal voltage around 3.6-3.7V. Plenty of folks get 2 or more days out of 3.7V 18650 batteries, so I'm not sure longevity is really a problem, at least in terms of time-between-charges.