The fuel cell produced power for about four days and had I needed more juice from it than I use in a normal day, the extra power was there. The Medis fuel cell was very easy to use and set up and simply worked. The only bad things I can say about the device is that you can’t refill the cartridge once its empty, it has an expiration date, you have to buy a new cartridge each time you run out of power and its rather bulky. You aren’t going to slip it in your pocket for a day of hiking with your iPod (unless you have really big pockets). The starter kit I tested here retails for around $40 and a replacement fuel cell is about $25.

http://www.i4u.com/full-review-519.html