Sony VTC5 for me..... I got mine from Mt Baker Vapor, because I had a $10 discount code, and I wanted to make sure they were real.
I've noticed that when I use my NC18650B pannys in the semo, they don't discharge all the way according to my nitecore i4.... but the vtc5 drains fully. (according to the charging lights)
18350 I've used the efest purple 10.5a... they work well, the red efest ones suck. The AW IMR are good too I'm told.
As for where, I think mtnelectronics
18650 - 26650
I've never bought from them, found out about these guys on a flashlight forum....those flashlight guys are as crazy (crazier?) then we vapers are about batteries.
Oh another note about the 3400mah pannys, somewhere I read they are rated at that mah down to 2.5v or something, so since our cutoff is 3.4v we will not be getting 3400mah out of them.... I dont know if thats true, but I read it on the internet, so it must be.
Last, vapordna has the vtc5's 3x $30, and somewhere there is a $10 off coupon for orders over $35, of course I can't find it now that I mentioned it
