Are the batteries in the Nintendo switch locked in anyway? Wonder if its viable that third party batteries could have an increased capacity.

There are definitely third party batteries, but the replacement process is not trivial for a typical person. Lots of adhesives are involved.

	▲	bigfishrunning 3 hours ago \| parent [-]
		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.