The Wind-Up Battery concept comes from the minds of Yeon Kyeong Hwang & Mieong Ho Kang. These two have developed a rechargeable battery that doesn't require any electricity to charge.
The Wind-Up Battery concept is eco-conscious and shouldn't break a sweat. To recharge the batteries, all you have to do is twist the battery consecutively until it's full. Though I'm not sure how many twists it would take, I'm sure it's worth it instead of going out and buying another pair.
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Sunny Eco Chargers
Enhanced Eco Batteries
Interchangeable Battery Packs