i bought a ego twist 650 and its huge compared to my ego-c upgrade 650, which is only 2.5 inches long and the twist is about 1 inch longer.. i can't imagine how long the 900mah+ VV
batteries are. i decided to stick with the smaller ego upgrade
batteries, i don't get full VV range, but at least i can switch to slightly higher volt (3.7) while keeping the device small as possible, i get decent vape at 3.7v, and get about 2 days of vape on my 650 and i have 3 of them (so far)...