So this evening, I was wondering if you could power a hamster off a USB port. Let's do a rough calculation...
A USB port is rated up to 500 mAmp and 9 V. This comes to 4.5 W, or 4.5 joules/second.
Per Nutrient Requirements of Laboratory Animals, Fourth Revised Edition (National Academy Press), a small hamster (45 grams bodyweight) consumes 109 kilojoules/day.
So, you'd need 6.73 hours to recharge a hamster for a day of hamstering via USB port.
So now you know.