The 3VO is a pretty inexpensive selectable voltage mod also. $48 base price. 3.7v on 1 battery. Stack 2 16340's and get 4, 4.5, and 5volt settings. I really like mine. It was my first experience with higher voltage. Although, I am still saving up for Provari for my 2 month celebration of being analog free. Tomorrow will be one month!!!!