Getting energy from everywhere

For a long time now I have seen several "unusual" ways to produce electricity but mostly never seen them in use in real life devices.

As somebody working with a laptop, I can tell that the amount of electricity used by my computer does not allow the battery to last for a long time (maybe 4 or 5 hours if I'm doing nearly nothing with bluetooth and wifi shut down and screen backlight set to the minimum, and about 2 hours doing more CPU consuming stuff).

Computer makers are usually working a lot on:

• making less power hungry computers,
• making higher capacity batteries.

But I thought more stuff could be done, add electricity generators in the computer:

• making electricity when pressing a key on the keyboard (keys with magnets/coils),
• adding solar panels on screen's back (maybe on the front with a transparent solar panel?
• use vibrations to generate electricity (several implementation exists using magnets, piezo-electric systems…),
• use temperature gradient (thermoelectric effect)

But then, we need to check the full energy usage here. If those generators cost more energy to produce and recycle than the "free" energy provided/saved, we should not use them.

My example was about a laptop, but those technologies can be used in lots of other devices (and several are already in use but not widely):

• In wall clocks with thermoelectric effect (temperature gradient between the wall and the air) and solar panels.
• In wristwatches with vibrations.
• In cellphones with solar panels, vibrations.
• In wireless keyboards with keystrokes.

Well, anywhere a battery is in use.