For mobile phone users, a flat battery or a lost charger are among the frustrations of modern life.
Now new research promises a way to recharge phones using nothing but the power of the human voice.
Electrical engineers have developed a new technique for turning sound into electricity, allowing a mobile to be powered up while its user holds a conversation.
The technology would also be able to harness background noise and even music to charge a phone while it is not in use.
However, there could be a downside to the innovation, if it gives people a new reason to shout into their phones as they attempt to squeeze in every extra bit of power they can.