The Aspire Pockex kit is a very popular kits. It is simple and reliable. The battery life is 1500mAh. 

PockeX Top-Fill Instructions:
1. Unscrew and remove the top cap
2. Fill your liquid into the tank 
3. Screw the top cap to the PockeX

Make sure when you fill the liquid you only fill up to the max line otherwise the liquid will overflow when you screw the topcap back on.