system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did the iPod Shuffle charge from a 3.5mm headphone jack?

I never see any articles mentioning how they charge, everyone is just concerned for it to BE charged. 

I mean, it would be lit if I could charge my phone through a headphone jack...

How does it work?
gpt
For charging a battery you just need two connections. The headphone jack always has at least two (sometimes more for microphones)
It is not common to charge via headphone jacks but nothing restricts you to do so. Apple has built a charger to transfer the electrical energy from 5 Volt DC to whatever the shuffle needs.