Does this happen with just one carto or all of them? Leaking is not normal, but a small amount of moisture will usually end up on the threaded end of the battery, which needs to be wiped out with a q-tip and/or tissue every time you change cartos and before you screw the battery onto the charger. I also clean the threaded ends of batteries with isopropyl alcohol every day or two.
If the carto is not defective and it's leaking more than a drop into the battery threaded end, you're overfilling the carto. It can take a couple of minutes for the juice to drain down into the carto filler. When refilling a carto, I'll drip in 10 to 12 drops of liquid directly into the filler, let the carto sit threaded end down for a couple of minutes, then add a couple more drops if there's no juice at the threaded end. I'll also blow through the mouth end to remove any excess juice and gurgling sound. Blowing through the mouth end also helps to drain the juice into the filler quicker.