Eventually, you will decide as most do that auto batteries aren't worth the trouble they cause. It's hard to seal an auto battery because air has to go in and out for it's diaphragm to sense when you draw. If juice gets in the hole, the next draw you take results in juice getting sucked into the vacuum switch.
Most of us use press to fire batteries. They are cheaper and much more reliable. Once you get used to pressing the switch (about a day) it seems very natural to do.
With few exceptions, we buy the batteries of our choice in the thread size we like and buy the cartomizers and atomizers to fit. 510 thread (eGo) is pretty much the standard with some preferring KR808 threads. if you stick with 510, you can find almost anything you want to fit it. KR808 is popular also with all the Volt style ecigs in use.
In case you aren't aware, eGo style batteries come in 3.4v and 3.7v designs. There's also the eGo Twist, which is a variable voltage eGo battery that is becoming very popular. With it, you get to dial in the experience you want with the atomizer of your choice and the juice you like. You can dial the voltage up and down to increase vapor and taste.