Because the battery is inline and because the battery stick has a chip in it the best you will ever get is 3.7 volts...you can use a .5a or 500ma charger with that passthrough because the power comes from the battery, not the wall...it acts as a capacitor...you CAN take the battery out of the equation like i did but then you need a 1.5a or better to even get a vape off of it...best buy sells a 2.1amp wall charger that works great but it is 29.99
but for your passthrough anything will really work...but i found that those suck...excuse my language...i could never get a good vape off mine which is why i cut the battery out and now it works great with the new wall charger....the voltage of the wall charger really isnt what matters...it is the amps...watts are really what we want and you can find out the wattage by voltage X amps...but then you also have to factor in the resistance of the atomizer...so it gets a little more in depth...i g2g but i will elaborate more later