Battery problem while recording videos.

I got my ipod touch 5 1 month ago. I got a problem while recording videos. The battery was around 40 percent, but after I recorded a video for about 1-2 minutes. The 20% was popup, then it turned off automatically. While I turn on it, the battery will be about 30 percent. It happened several times. Is this normal?

Does anyone have the same problem?

Thanks!