Hardwired USB Passthrough

[Ken_A]

I can't reasonably recommend you use a passthrough while driving.

I do all the time... On long trips. Beats fumbling for a new battery anyway.

 

[WarHawk-AVG]

I call them a USB bypass...no battery to "passthru"

I bought 4 of these...5vdc, no variable voltage capability (I use 2.8Ω or higher heads [they came with 2.2Ω!!)
Energy Saving 900mAh Electronic Cigarette USB Rechargeable E-Cigarette - Stainless Steel - Best Deal | aHappyDeal

fasttech has variable voltage ones
$5.50 Variable Voltage USB Passthrough Battery for E-Cigarette - silver at FastTech - Worldwide Free Shipping

Careful the cable isn't attached to anything...merely held with a glob of glue and if you pull it too hard...it will snap the little wires