> You can't make batteries out of nothing. We can always discover new physics, or utilise already understood physics to design something more efficient. Like w

> You can't make batteries out of nothing. We can always discover new physics, or utilise already understood physics to design something more efficient. Like what if your phone was efficient enough that it could work only on the heat given off from your hands and/or ambient light? Sounds far-fetched but I won't be surprised if this is commonplace within the next 50 years.