My mobile phone is out of battery.
My mobile phone is dead.
My mobile phone has run out of charge.
My mobile phone has no battery.
My mobile phone ran out of power.
還有老外會用比較口語化的「The cell phone is out of juice」，如果是快沒電了，就用「battery is low」或My cell phone is low on battery。
It's charged up(充完電).
Mike: Hi, Bill. I called you at your cell phone but it had no response.
Bill: Sorry. We are losing the signal.(收訊不好) I can't quite hear you. The reception is really bad in the basement. What's up?
Mike: What was that again? (你剛說什麼) I am losing you!(我聽不到你的聲音) Hello….
Bill: I'm sorry. The call just got disconnected for no reason. (莫名其妙就斷線)
Mike: that's okay. Where were we? (我們講到哪裡?)
Bill: You are breaking up again! (聲音斷斷續續)
Mike: The signal is too weak here. (訊號太弱) Anyways, I will meet you at 5:00 at your place.