1) The second option is more specific and more literal, but in conversational English, option a) is more likely what you will hear. Both are correct, but the first option is more common and sounds more fluent. 2) Yes! All those look good. One thing that sounds more colloquial, though, than "has run out of power" is simply "ran out of power." It's still correct, though. :^) 3) "The battery is dead" is another way to say "the battery is out of power." If you say "my phone is dead," you are saying that your phone is out of battery power. If you are having a conversation with someone, saying "my phone/tablet/device is dead/died," you will sound more natural and fluent. Hope this helped!

Hi! I didn't understand the first sentence. What is the device which needs charging? The bluetooth headset, the mobile or the tablet? The second sentence is "The battery of my...." Sorry but I'm not able to answer at the 2nd question... The third means that the battery hasn't power, it needs charging. In Italian we say "Il mio cellulare è morto. (My mobile is dead)" when it's broken so it doesn't work or when it needs charging. Hope I was clear!