Out of juice

This expression is a slang way to say that something (or someone) has no power or battery left.
Depending on which country you are in, you may also hear out of gas or out of steam.

Example: Oh no! I need to call the office, but my phone is out of juice!

人や物のパワーや充電が無くなってしまうという意味のスラング表現です。国によっては、「out of gas」や「out of steam」という表現もあります。