Charge it until the button light goes out, then it's fully charged. The charger is about 500ma, or 1/2 amp, so it will take some time. You will get between 300-500 full charges before the battery peters out. I have the CF model where you can use your own 18650. I mount up my Big Dripper and go for the day (with a spare 18650 just in case).
I also have an Ego One Mega in black. 2600Mah (22mm), charges via USB. Fires down to .3. With the CLR rebuildable/rewickable heads, that squat Ego Atty just does the trick. At .5 with the standard CLR heads, it put out admirable vapor for a "beginners kit". I wish I had one like I do now when I started vaping. 901 Atomizers and those fucking cartridges just sucked, but that's what was available.
The Ego One Battery is also a good one to get, not as cheap as $25, you have to get the kit - the atty is good on it's own and great for a backup, but it's got the advantage of being able to charge via USB with 1 amp wall plug, cutting down the full charge time to 2-3 hours.
Plus it looks killer with my Lemo Drop in black with a smoked tank. All evil and dark Vulcan kinda thing
