If you are using automatic batteries you want to be very cautious about refilling your cartomizers. We only recommend the "pop-a-top" method when using automatic batteries. Any excess liquid that seeps out through the battery connection will quickly find its way into your battery switch and destroy it permanently. This is what usually happens if you use the "push" method.
The "Push" Method
Now onto the "push" method or what some people have nicknamed the "condom" method. This method is ONLY RECOMMENDED when using the cartomizers on a sealed connector battery, typically pushbutton, or a "mod" with a sealed connector and leak proof cap. Look if your batteries have a button, If they do, then that's a manual battery and this method is safe to use.
You will need one of the rubber cartomizer covers without the center seal to perform this refill method.
While holding the cartridge with the connector end towards the cartomizer cover, insert it carefully and without blocking the hole in the top cap, slowly press the cartomizer down fully into the cover. This forces the e-Liquid up into the cartomizer through the air hole in the battery connector.
Once fully seated into the cover, carefully remove the cover and with a papertowel clean any excess e-Liquid from the cartomizer and especially the battery connector area. You're done!
PROS: Super easy to do and nothing to take apart or break.
CONS: No way to inspect cartomizer internals to check for possible degradation. Automatic batteries are at risk from the damage caused by excess e-Liquid in cartomizer connector.
The "POP-A-TOP" Method
This involves popping the white end cap out of the cartomizer and refilling it directly into the wicking material. To remove the cap insert a hard steel object like a pin or a small screwdriver head into the hole. Work the tool in a circular motion while prying up. This will break the glue loose. Once loose just remove the cap and set aside. If you happen to break the end cap, don't worry..! You can still use the cartomizer without the cap and for some people this is easier because you can easily "top off" the cartomizer with more liquid if needed. On some cartomizers there is also a rubber washer beneath the cap. Remove this by gently prying out and also set aside.
The best way to fully fill this cartridge is to place the tip of your e-Liquid dropper tip on the side of the cartomizer and let it flow down the inside of the cartridge body and into the wick. Concentrate it to one area until you see the wick material become saturated all around. If you fill all over the top then you may trap air beneath the top and the cartridge won't fill completely. If you overfill the cartomizer, simply place the open end into a papertowel and blow as hard as you can through the battery connection end.
PROS: Easy to do. You can see the fill level. Ability to somewhat inspect the condition of the wicking material. Easier to guard against overfilling if using automatic batteries.
CONS: End cap may break during removal and not be re-usable. A little more work than some people want to do.
Refilling the cartomizers may sometimes vary a little depending on the E-juice. Just like shown in this video: