Well, my PSP had its battery inflate. I had replaced that battery a few years ago, used it a bit, then forgot about it. Recently found that the new battery is in oopsie state too.

That's sad :(

Did you store it in a too hot place or leave it with zero charge for too long? I only had a few devices with inflated battery so far, and I scrape a lot of. My stuff and the stuff I get from people tend to be in a relatively good shape even after staying unused for some years. E-readers are the champions of battery preservation. I got one from a friend that was forgotten for more than 10 years, and it works well. He said that the battery originally lasted more than a week. Now it's lasting only about 3 days, which is a huge difference, but not enough to make it unusable.