Why arent the 5th Generation iPod Video batteries (30GB 550 mAh and 60GB or 80GB 850 mAh) interchangeable?
To understand why the batteries are not interchangeable, you must first understand a little bit about the internal layout of the iPod Video: The battery inside the 30GB, 60GB, and 80GB iPod Video lays alongside (not on top of) the hard drive. Since the hard drive inside the 60GB and 80GB iPod Video is almost twice as thick as the hard drive inside the 30GB model, there is more physical space for the original, stock battery (and our 850 mAh battery). Since the hard drive inside the 30GB iPod Video is thinner, there is less physical space, which is why a thicker battery like the 60GB and 80GB 850 mAh battery just won’t fit. Lastly, the 60GB and 80GB iPod Video offers more playtime and therefore demands a more powerful battery than the 30GB version could provide.
