I started with the small e-cig and small batteries and it drove me NUTS! I was always waiting for a battery to charge and a couple times it caused me to smoke. I considered what I wanted and researched and came up with the 1100 mah eGo (cheapie clone) passthrough battery. It has a USB cable connection on the bottom and I can still vape with it even if it is charging. The USB can connect to a computer USB2, a wall adapter or a car adapter, and you never have to touch the batteries. The 1100 mah will last all day, is strong enough to drive low resistance devices, and (as noted before) it is 510 threaded and eGo threaded so you can use most anything with it. I use the Star Dust clearomizer. It has a screw top so it doesn't leak or slip off, can be filled easily from the squeeze bottle, and has eye appeal with the eGo battery.

The main point was the price.
canvape has the 1100 mah passthrough battery and USB charging cable for 20 bucks and the Star Dusts for 5 bucks. Two of each (plus a spare to share between the two of you) and a selection of clearomizers to try out would still be under $100. And you have skipped several generations of eGo systems.
Worked for me. YMMV
And of course there is always the top of the line Darwin, if money is no object. Don't ask what the top of the line is, everyone has a different opinion. I am just happy where I am and the passthrough batteries cost me less than I spent on the small ones that satisfied me 90% of the time. Of the many ways I have tried to quit smoking, vaping is the only one where I
forgot about it, and that was with the large batteries. It's that pleasurable!
Keep your wick wet.