When it comes to refilling the cartridges, although it is a very simple process, we strongly recommend that you fully understand the process of refilling cartridges correctly because the spill or leakage of liquid on your hands or mouth could be dangerous. There are many Youtube videos on the Internet, which demonstrate that process. We recommend you to check them out and understand the process well before doing it.
In general, just open the white cap at the back of the cartridge (using a pin or a pen), turn the e-liquid bottle upside down onto the cartridge and drip a few drops of e-liquid. Be sure to hold the cartomizer at an angle as liquid dripped into the center tube will leak through the battery connector. Repeat the process until the filler material no longer absorbs liquid. In general, about 20-drops (1 ml) are needed per each refill. The first refill in a blank cartridge may require more liquid (20-25 drops). As the filler material becomes more saturated, it takes longer for the liquid to fully be absorbed. Therefore, a wait of several minutes toward the end of the process may be required to ensure the material is completely wet.
Dripping too fast when saturating the filling will result in liquid seeping out the battery connector end of the cartridge. Keep the battery connector end covered with the silicon rubber caps, often referred to as condoms, when filling to minimize leakage.
Put the white cap back and you should be back in business. Sometimes it is not a bad idea to let the cartridge sit for an hour or so to get the liquid completed soaked in.
If you are getting burnt smell and/or no vapor after filling the liquid, try adding a few more drops in the cartridge.