My echo-e battery is 1300 mah and lasts all day. I also have a Riva battery that's a 1100 mah battery that lasts all day too.
The echo cartomizers are really big, they hold like 3-4 ml of juice. I don't really need a carto that holds that much juice and I think because they're so big, the draw is a little tight. I found this with the ego megal dual coil cartomizers too. I use the smoktek cartos that hold about 2 mls of juice.
I can't really point you to where I got mine because I got my kit from a member here, Bill that became a supplier and he's ill and isn't selling anymore. But I really like the echo-e batteries better than any batteries I own.
Here's the echo thread.
http://www.e-cigarette-forum.com/forum/ego-type-models/189567-echo-thread.html
I would check there about the adaptor or where to get a kit. Good Prophets and Mad Vapes sell adaptors but I'm not sure of which adaptor you would use.
There is also the KGO. That has a big battery as well. BreezeSmokes has the KGO. Sweet-Vapes (use the dash) has a good deal of 1100 mah battery Riva kit.