battery over charging, Please help!!!

As my post eariler, I disconnectd the negative of battery and reconnected it 5 minutes later, the battery was occur high votage (17.2V something), so when it was on high votage, the acceleration wouldn't go smoothly, then I turn on the high beam, fog light and air contiditioner, the votage went down to 13~14 Votage, then acceleration went smoothy, but after I did couple times of full throttle acceleration, the votage went back to 17 something votage, and acceleration didn't go smoothly(like what I mention above). the terminal of battery is clean, so I am wondering why it became like this after I reconnect the negative of battery. is it possible the genarator's problem(like over charging) or some other problems?

Best/Wish
Stephen