Alright, so I went back to Dan, and I asked him to clarify.
That being said, Apple would also run a more comprehensive test for you at no charge at an Apple Store.
It is just a characteristic of the lithium-ion batteries in laptops and nearly all modern electronics.
That leads to greater battery life.
To me, you might as well have had a shitty battery that only had 20% worth of charge anyway then, minus all the conscious effort that you need to make to take care of it.
I try to provide the most helpful updated content on this subject.
So framerates will be substantially worse when playing on battery expect around half.
Were you worried above overcharging your AirPods? Apple Vice President of iPad Marketing, Michael Tchao, has set the record straight on allegations that the either fails to report the proper charge level, or over-charges and risks damage if left charging for too long.