There are definitely third party batteries, but the replacement process is not trivial for a typical person. Lots of adhesives are involved.
Also, third party batteries vary wildly in quality -- I've replaced the battery in my Nintendo switch twice, both times using brands I've heard of, and neither battery is as good as the original OEM battery was when i first got it.
Also, third party batteries vary wildly in quality -- I've replaced the battery in my Nintendo switch twice, both times using brands I've heard of, and neither battery is as good as the original OEM battery was when i first got it.