My Sony Ericsson T200 cell phone is ~4 years old. (I know, vacuum tubes and dial knobs). It is no longer made. Thus, they no longer make the batteries either. My battery's life has become quite short, lasting only a day or two without use (it used to last all week), so I'd like to replace it. A guy at the Fido booth suggests that I can get an aftermarket battery, but those batteries will not be nearly as good as the original (I don't know if he means because they're old or becasue they're knock-offs). Anyway, the number he threw out was 30%, meaning I might only get 30% performance out of them (which is about what I'm getting now). My question: are these after-market batteries less able to perform - for whatever reason - than my original?