I have never cleaned the battery but I frequently clean the mod. There is a black ring on the bottom of my battery does that mean anything? And i think so because I let it fully charge. And probably about 5 battery cycles and a few weeks
Clean your battery ends with just a bit of rubbing alcohol on some vaper towel. Get the switch contact and top post too while you are at it.
Then, break out your multi-meter and check to see if your batteries are truly being charged to 4.2v. A trustfire charger is anything but trustworthy. Verify that it is working properly. If it is overcharging, it may be killing your batteries in short order, under charging, your batteries might still be ok.
If you don't have a meter, get one. Anyone using a mech mod and RDA's needs a meter or three.