I'll tell you what's great about this 510 / EGO threaded eCig battery, it's compact (94mm total length) so it fits nicely in your pocket but with a massive 2200mAh capacity. The manufacturers tout this as a "1 Week Battery" however if you are a heavy vaper like me then 2-3 days is probably more like it :)

Also has a very useful power level display function, the button changes colour from White = over 60% remaining, to Blue = 60 - 20% and Red = less than 20% or as I like to call it "don't leave home without a spare battery!

Overall a very nice battery with great build quality and capacity for a fantastic price, this is now my battery of choice for everyday use...