I personally use a Sanyo UR18650FM cell that i salvaged from an old laptop battery, got 3 good ones and throwed 2 away. Tested all what I got from the pack and the three good ones all read 4.2 volts. These are actually good batteries too, I've been using all of it with a .7 ohm coil and it's firing at 25.2 watts with a 6A current. According to the internet, these are 2600mAh, and that's a pretty high ampere for an IMR, so I'm kinda assuming these are ICRs. They are really good though, it seems like they could handle 6 amps pretty nice, and they give me a good amount of vape time before I feel it's somewhere below 3.5 volts. Before I used these cells though, I've been exclusively using the Black Efest 2250 IMR High drains exclusively with my setup, and these are very good batteries for a SLR setup too.