ipod touch 6th generation with swollen battery

In that case I think you should contact Bose and find out if they have any opinion. If it helps, mention this discussion, although I do not speak for Apple, nor do I carry any weight with Bose. I'm simply a fellow user of both Bose and Apple products.

My personal opinion is that to have one swollen battery is unlucky, to have two is unusual, but to have three means that you need to get to the bottom of the issue.

I don't see how anyone can offer you a definitive explanation.

Perhaps all you can do is rule out anything you might be doing.

• • are you using an unconventional charging method or a basic USB charger? In other words, how do you charge your iPod?
  • are you leaving the iPod in a hot place, such as a car? Even on modest sunny days, the temperature in a car can become very high, which is not ideal for the battery
  • have you dropped the iPod, either causing significant damage to the casing (a dent for example) or simply just a very severe drop onto a hard surface. Either situation may have dented the battery, which could cause it to swell
  • is there anything else unconventional that you might be doing?