Most old PC laptops have external batteries you can detach by pulling out on a springloaded tab. Even MacBooks are possible to run without the battery, but it requires some NVRAM trickery IIRC.

Some older MacBook and MacBook Pro models reduce processor speed and GPU performance roughly by half when running without a battery, to avoid shutting down if the computer needs more power than the AC adapter can provide.

Apple documented the behavior in a support note. I’m not sure if the Apple Silicon models do the throttling as well. I guess the situation doesn't come up as often since the batteries are no longer user-removable.