When you use an e-Cigarette, you want to keep the brass threads of the eCigarette rechargeable battery clean. The e-Cigarette battery screw threads will become dirty after a period of time.
Some manufactures use batteries with female screw threads.These manufactures then use male screw threads on the nicotine cartridge. This makes it extremely difficult to clean the screw threads of this type of battery. Yes even with a 3-part system,the 'reusable' nicotine cartridge will need to be replaced after extended use. 

It is much easier to clean an eCigarette battery with male screw threads and female screw threads on the disposable cartridge. To clean your eCigarette battery screw threads you will need: one paper towel, one Q-Tip, and some rubbing alcohol.

Fold the paper towel in half and simply dampen a small portion of the paper towel with the alcohol. With one hand grasp the body of the eCigarette battery. Place the dampen portion of the paper towel around the exposed male screw threads and grasp firmly.

Simply twist the battery as if you were attempting to screw the battery into the damp paper towel. Next, twist the battery in the opposite direction as if you were unscrewing it from the paper towel.

Now, force your thumb nail into the paper towel and between the screw threads of the eCigarette. Screw and unscrew the battery several times. You will probably be amazed at how much black stuff came off of your battery and is now on the paper towel.

Once you're finished, it's time to clean the end of the eCigarette battery. Stick your Q-Tip into the alcohol and then 'scrub' the brass tip.

You will always know when it's time to clean the brass threads. It becomes more difficult to obtain a smooth and easy puff on your e-Cigarette. After you have cleaned the brass threads, you will be amazed at the smooth and even draw of your e-Cigarette.