You may have very well gotten a bad battery. The quality assurance is very high at SureFire. I have B20, B90, and B65 batteries. I probably have a dozen of the various types. I have never had a failure.
The B20 batteries I have come with a protective cap. The cap protects the contacts of the battery, and I suspect keeps the lubricant from collecting debris. I have neglected the O rings and had one fail. That experience trained me to maintain O rings properly.
The fast charger is a slight bit finicky, and takes some time getting familiar with.
Good luck