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A YouTuber going by Flamethrower spent nights listening to his brother's new hamster squeak through the exercise wheel and decided to harvest the energy. The result is a working phone charger powered by the rodent.

A hamster runs in bursts, while a phone wants steady voltage — that's the engineering problem. Flamethrower's rig handles it with a Texas Instruments BQ25570 energy-harvester chip, the same family of parts used in solar and wind setups. The chip cold-starts at 330 millivolts and uses maximum power point tracking to feed whatever the rodent is doing into a salvaged lithium-ion cell. The motor came from a broken broom. The 40 cells came from an electric scooter his brother had taken to a repair shop because the battery was "broken." Every cell, Flamethrower says, was fine.

The phone charges. Slowly.…