Some laptops intentionally slow down when they are running on battery.
Projeto de documentação do GNOME
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Rodolfo Ribeiro Gomes
rodolforg@gmail.com 2011

# Why is my laptop slow when it's on battery?

Some laptops intentionally slow down when they are running on battery in order to conserve power. The laptop's processor (CPU) switches to a slower speed, and processors use less power when running slower, so the battery should last longer.

This feature is called CPU frequency scaling.