Another great thing about the in-line battery on a usb pass-
through...  Very few USB battery packs put out the power needed to fuel the pass-through.  The Kensington is one... 1.5A, but at around $50.  Most are underpowered. 
But...  I picked up a Lenmar for $15.  It only has 700mA output, which doesn't provide enough power to fire up an atomizer.  But it IS enough to recharge the in-line battery.  Soooo... I '
vape' on the in-line while it is recharging from the $15 power pack.  Saved lots of money, and works like a champ.
Same thing with USB adapters for your car.  They don't put out enough to fire up the atomizer, but work great with the in-line battery pass-through.