Replaced the dead battery in an old iPod Nano I bought (really wanted a cheap Product Red one) and not even 2 days later the replacement battery expanded. I would call this
For Apple iPod Nano 6th Generation | Replacement Internal Battery Pack
Battery 616-0531 616-0640 Nano4 For Ipod Nano 4 6 4th Gen 6th 7 7th 4 4th Gen 8gb 16gb Mb903ll/a;616-0639; [w0784] Mp3 Mp4 - Mobile Phone Batteries - AliExpress
iPod Nano 6th Gen Battery Replacement From Start To Finish. - YouTube
Sinbeda 330mAh 3.7V Li-ion Battery Replacement for iPod Nano 6 6th Gen 8GB 16GB for iPod Nano6 Battery 330mAh - China Li-ion Battery and Replacement for iPod Nano 6 price
For Apple iPod Nano 6 6th Generation Battery Replacement 3.7V 105mAh 616-0531 | eBay
NEW Battery Replacement 3.7V for Apple iPod Nano 6 6th Generation Gen 616-0531 647213053951 | eBay