I have a 901 paathou tested with a volt meter and run's at 4.89v I also have a 901 vp1 tested with the same meter and run's at 4.02v fullycharged. But the vp1 at lower volt's knocks the sock off the passthou for vapor and taste. ? WHY ? I just don't understand. Is there something wrong with my passthou or is my vp1 just magic? The volt readings were taken at the battery connector's, And the same atty and e-liquid was used to compare. I also gave 2 min's between device change to let the atty cool all the way. Also I tryed in this order passthou then cool then vp1 let atty cool for 15 min's then vp1 let cool passthou and the vp1 just does abetter job makeing vapor and taste.. And two drops e-doobed onto the bridge per test with no filler in the cart. (EDIT) I retested with a friend's computer running the passthou and it was 4.91v and the vp1 still did better. And the battery in the vp1 was not recharged for each test.