One day my phone died completely so i fully charged it. And then I found that the battery was draining like crazy.
So I took out the battery and then put it back in and it won't turn on. So I plugged it to the charger andit turned on! And still had power. What's wrong with it? I've already installed new os and it didn't work. Help me!
Sounds like the battery is still not charged, and it only turns on because you've got the charger plugged in. Are you using a Blackberry branded charger & cable? (If not, you should be.) Is the battery actually charging steadily while the charger is plugged in? See if little battery icon is in the upper left corner of your desktop.
Also, open the Device Monitor and see which apps are using the most battery power. You may have some headless apps running in the background which you're not aware of. Close all running headless apps, and any running browsers and audio/video apps, and see if your battery will hold its charge that way.
One more thing, please include your OS version when you post questions like this. You could be using the wrong radio or an older OS release too. (Type "myver" to see which version is running on your phone.)
Hope some of that helps!