I have a buz pro that stays on 4.25 volts for three different cartos, sometimes I crank it up in the morning to get a quick fix. Never made a 5v mod , could probably do it but don't have the electic know how for resistors. some one should make some tube mods with two batts that are regulated to 4.25 volts. no muss no fuss just the sweet spot. A box would be cheaper and would be ok as long as it wouldstand up with a tank on it.