I really like EVODs but only with higher resistance coils and mostly with reducable voltage batteries. Otherwise burning on the long drags that are needed, although I have tried them on my mech with cotton wicking to keep up and that's cool, no hit timer! I've had luck with some real cheapie batteries.
Guessing, not that I keep good track, you should be able to get a tank at least on a 650 maH battery, if you don't battery is crappy, but if you're using multiple tanks a day you need something a little bigger, say a Spinner 1600 maH (clones may claim 2200). Or just carry enough.