So that's the differenece between official battery and third-part battery

Until now I didn't know what is the problem of using third-party battery for devices like my camera (my Canon PowerShot SD880 IS camera, to be specific).  But a while ago, I took out the camera which I haven't touched for months (in fact, probably half a year), and found that while the third party battery was almost dried up, the official battery that comes with the Canon camera still has about 80%+ battery level, and it took no time to get charged back to 100%.  So there you go, that's why you should buy the official batteries.