The Toshiba methanol fuel cell could power a mp3 player for 20 hours. The fuel cell works by mixing methanol with air and water to produce 100 milliwatts of electricity, which can power an mp3 player. Toshiba already showed off a Fuel Cell to power Notebooks last year. Hitachi has a Fuel Cell concept for PDAs.
More details in Toshiba Press-Release (japanese) and on BBC News.
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