[causality0]

I'm surprised they don't sell some kind of reciprocating dynamo-type thing for hikers to strap to their knee to charge while walking.

[shard]

Doesn't that just increase resistance to your walking, thus is equivalent to you converting calories to battery energy? Wind and solar would be additional energy over what you brought as stored calories or food.

[rowanajmarshall]

Going by a random Reddit thread [1], it takes less than 5 calories to charge an iPhone. I think that kind of device is already on the market though.

You're not gonna power a heater or aircon through body movement, but devices should be fine.

1. https://www.reddit.com/r/theydidthemath/comments/693daq/comm...

[Dylan16807]

It's just a unit conversion, you don't need to cite reddit.

A Calorie is slightly more than a watt hour.