I agree with Ken's Box mods. Great customer service. I have a couple of the 3.7 V ones. I use Ultrafire 14500 900mah with them.
As for your short battery life, it's due to your using dual coils, not the battery. 900 mah is 900 mah. If you use conventional cartos with a higher resistance, like 2.6-2.8 ohm, your batteries will last longer.
As for your short battery life, it's due to your using dual coils, not the battery. 900 mah is 900 mah. If you use conventional cartos with a higher resistance, like 2.6-2.8 ohm, your batteries will last longer.