This past November, my daughter's 3G 20GB iPod died. No AppleCare, three weeks after warranty. According to our local Genius, it was a hard drive failure, as the iPod gets quite warm when you plug it in to charge, but there is no disk activity to hear and no display function. Rather than spend $249 to get it repaired, we opted to get her the U2 model. Now I've got a mostly useless (won't play music, but at least it makes a good paperweight) 3G iPod sitting on my desk. I also have a perfectly fine 4G in my pocket. Is the 3G battery compatible with a 4G? Even better, are there other, less expensive repair options out there to get this thing running again?