It is super easy to pop the top off Vapor4Life cartos or any soft-cap cartos. Use an unbent paperclip and stick it in the air hole only far enough to pop out the cap. Even easier - use one of Vapor4Life's drip tips or you can get get plastic or delrin KR808D-1 drip tips at LiteCigUSA.net. Don't drip juice into it - it would aim right for the air channel. But it makes a great easy-to-remove mouthpiece and keeps your lips cool too.
Video of a first-time filling with extra stuff like straightening the air channel (skip that unless your carto needs it). I usually hold a tissue on the threaded end. When done I make sure it is not dripping, clean and dry. Then I puff into the threaded end to clear the air channel of any juice that accidentally got in there. After the first fill or any large fill, you may need to let it sit so the juice can distribute into all of the stuffing - especially on the first fill. You don't want to vape these things dry - you can singe the stuffing and then the flavor will be bad. Keep it damp and a cartomizer can work well for days or longer.
I need to get the video link...
Great video - and I just use an unbent small paper clip for everything. And I usually rotate the carto when filling and go a bit slower because the stuffing seems tighter these days. The channel straightening part will come in handy if one starts dragging hard and you can see the air channel got crooked (when you can't see light all the way through)
http://www.youtube.com/watch?v=8pyzOGQ0tMo
For soft-cap cartos see Vapor4Life (prefilled and 2 kinds of blanks) and see the Premium KR808D-1 blanks at LiteCigUSA.net and others. There are also more exotic reservoir-type cartos that require a particular kind of syringe to fill (see Gotvapes for those).
Re batteries - I recommend standard manual Vapor4Life or plain manual KR808D-1 from VaporLeaf.com, LiteCigUSA.net and elsewhere.