You need to ask yourself - where and how often will I be using my e-cigarette?
For everyday use, you should not be buying a small battery - it is a smaller design and looks more like a real cigarette but it needs re-charging far more often which means you will need to replace the battery more often. In addition, it will be less effective at vapourizing the e-liquid. Any battery below 650mah for everyday use is a bad idea. Most popular for everyday vaping are the batteries found in our eGo C and eVod kits.
For occasional use, when you are out and about, a smaller battery is a good idea as an e-cig with a smaller battery will be smaller and easier to carry around. We would recommend a 250mah - 350mah battery in this case such as the battery found in our 510T kits.