[noobermin]

Arguably, yes. Of course, the power requirement to recharge a battery for a calculator (in a decent amount of time) is a lot less than that for a modern cell phone. Same physics if your level of detail is Ohm's Law but very different in practice because we are talking about charging a phone batt in a comparable time to plugging it in.

[mitchty]

Yeah, kinetic energy recharge of a phone is a pipe dream, last time I remember figuring out how much energy you can get from that, it amounted to walking across the USA from coast to coast.

Solar is equally crappy.