I do not consider it an upgrade but an alternative to the mechanical v2 and v3. V2 and V3 can use different battery combos to get 3.7v, 6v, or 7.4v. The new v4 has a very limited voltage range 3.2v-4.2v and only works with 18650 battery. No options for HV atomizers/cartos. Seems like high...