That battery looking thingie is a battery thingie. =)
Some PTs use an inline battery. The purpose is to prevent the full 5 volts from the USB to feed the atomizer. If you are happy with the performance of your eGo then you can choose a PT with an inline battery.
However, there are (at least 2 that I know of) PTs that utilize the full 5 volts (no battery looking thingie). PureSmoker has probably the best one out there. It's the Cadillac of PTs with a heavy duty cable (most of these China PTs have a life expectancy of a few weeks because they are so cheaply made). PS's is USA made which you mentioned is important to you. (and me, FWIW)
PureSmoker.com - USA Electronic Cigarettes & USA Made eLiquid!!!
You might want to check this one out too...
THE VP-PT (USB PASS THRU)
Both of these are high end items, Audio. There are a gazillion places where you can buy MUCH cheaper ones -- which may not be a bad thing until you decide if you like it or not.
I'm not a PT expert. Hopefully somebody will jump in here with more experience than I have with them. I have just one that I rarely use and it's a cheapie. I only mentioned them because you said you're in the car often... for you it sounds like a natural. =)