Phone acting funny, ideas?

Okay so I have an Android phone. A few hours ago I was using it and it was fine. It charged overnight, so that's not a problem.

Then I went to do something, came back to text someone and it was frozen, but then I noticed it was actually off. Confused I turned it on, it said the battery was dying, gave me the notification and everything. Even more confused since it was fully charged ten minutes ago I turn it off and take out the battery, inspected it, and it was fine. I put the battery back in and turned it on again. And now it says the battery's full. Confused but grateful I go and do some things and then check my phone, it's on, I go to unlock it to text and it turns off while the battery still says it's full.

I tested the battery in my old phone where the touch screen is shot, it's not the battery, it's fine.

I can still play music and everything. (When the battery is low it doesn't let you play music or view images to preserve the battery)

As of yet it hasn't turned off again. Is this a common bug with androids or did my phone get messed up somehow?

Confused?

It is on warranty?

Yeah. It's only done it once since then.

I'd give them a call then. If it's not the battery, it might be something wrong with the phone itself that you can't fix on your own.

I figured I was just hoping that I wouldn't have to do that, because last I heard my phone carrier doesn't carry this model anymore.

What phone is it specifically, if you don't mind saying?

It's a Samsung Intercept.