iPod 3rd Gen Battery Replacement Went Great
The prior replacement battery (not purchased at iFixit) was never a good one. It was rated at 600 mAH, and never really worked right.
Battery replacements on the 3rd gen iPod is pretty straight forward. Cracking the case open is the only tricky part of the process. iFixit's replacement battery is 850 mAH and is a good one. I'm "training" the battery with some deep cycles, and it's doing fine.
Don't buy the cheaper batteries elsewhere. This one is reasonably priced and far superior, and is less expensive than others having a lesser rating.