Laptop power off the grid

When there’s no AC mains around, there are several alternative ways to power a laptop. However deciding what’s best is not so easy - it’s not about electrical power alone. Weight, size, safety, cost of and environmental concerns are all part of the equation. Here's an overview of alternative laptop power options when traveling off the power grid.
 

Alternative laptop power overview

Here’s an overview of alternative laptop power options each explained in separate sections. Renewable energy sources are covered in laptop eco power.
 

 
The Machine is equipped with all of the above except for the fuel cell.
 

Powering a laptop – the basics

Laptops have little to no protection to anticipate and stabilize voltage fluctuations. Therefor a stable, clean and reliable DC power source is important. DC power is usually delivered by 'switching power supplies' capable of generating ultra stable DC voltage. These devices are tested to the max, shown by a plethora of certifications printed on the back.
 

Most laptops run on voltages between 15 - 22 Volts DC – which are strangely high values for computers. Most chips require only 3.3 to 5 Volts. So why not a more ‘compatible’ voltage?

First if a laptop voltage would require just 5 volts, the current would sky-rocket to ranges like 10 to 20 Amps. Secondly, a laptop battery outputs about 11,1 volt and requires a higher voltage to charge at a considerable current. The conversion would generate quite a bit of heat inside the laptop from 5 Volt upwards. So the higher but odd input voltage is a compromise and over the years seems to average between 15 - 22 volts.