a) It is perfectly possible to include a battery, that, even degraded over some time, can provide enough peak power. b) They could have sold their approach as a feature. Or they could have included a warning: Slowed down, replace battery. Similar to what they do now. But no, they kept it secret. Ask yourself why.

Also, if you have that functionality, why crash and then display a message. Write: Crash prevented, but clocked down. Look what a Raspberry PI does: It flashes an icon if the power supply is not keeping up.