What is the acceptable verb to say that your battery has no energy (and I need to charge it)? I though on saying "My battery is finished" (and I need to charge it). This option is Ok? I've never saw English speakers in such situation so I didn't study from them about it.
In the UK, flat- (of a battery) fully discharged; dead. For mobile phones, etc, dead is becoming more widely used.
Depending on the exact circumstances, your battery could be
For a rechargeable battery as in a cell phone, you probably want (completely) drained.
For a rechargeable battery, I would not call it dead if it was still capable of being recharged.