Your problem is not your eGo batteries, it's their cartridge system, which they try to call a "tank system".
Get some 510 Kanger cartomizers and use them on your eGo batteries.
Other than the relatively low 3.4V of the eGo, there's nothing wrong with the batteries.
What you put on the end of a battery is the most important thing. The battery just provides power.
The best battery in the world would still perform poorly with an eGo-T or eGo-C "tank system".
Just get a decent 3.7V battery, whether it's a one piece, like a kGo, or takes separate replaceable batteries, like an e-Power or some mod.
Then, get some decent cartomizers or clearomizers. I recommend Fluxomizers for the cleanest taste and no filler to burn.
Find out what juice system works well before you waste a bunch of money chasing the latest "flavor-of-the-day" battery that still won't make a bad carto or bad juice taste good. As long as it's adequate, the battery is the least important part of an e-cig system. Volts are volts. It's what you do with them that makes the difference.