It's been my experience that it is usually the threads on the battery that are messed up. I find about 10-15% of the 510 batteries have this issue. Some cartos screw in and others won't, but it is not the cartos. When I find this I can take the carto and screw it into another battery and it works just fine. A battery like this will continue to give you problems. You can work with it using only cartos that will screw in and get another battery for one's that won't. I have a tap and die set and have checked the threads on several cartos that would not work in a battery and always their threads are good. Unfortunately, the battery threads are to shallow to tap. I have had some success threading cartos in and out until they make good contact, but it's a pain.