Why do my controllers keep disconnecting?

I've done countless Google searches and scoured this thread, and I've seen some recent posts to this thread with a few replies so I'm hoping this gets noticed. So I have a few controllers, 2 of them work pretty well, and 2 of them don't work so well. I am absolutely positive this is not an issue caused by the battery contacts as every single thread on similar issues seem to suggest. Whenever there is a button press or stick movement my controller will disconnect and then cycle and reconnect after an unreasonable amount of time. I don't know the ages of the controllers because I just don't have that kind of memory, but the two that have consistent issues are the classic white and grey, and then the black, and the two that work are new(er) models I think. I have taken them apart, so the possibility that I might have done some small damage is possible, but I wouldn't know what to look for if I did because I took them apart a while ago.