I remember, and I’m gen z. And some higher end laptops had two battery slots so you can hot swap the batteries without turning it off.
Those were the days. Everyone talks about how smartphones nowadays get people addicted to instant gratification and convenience, but IMO the ability to swap out the battery when it died was a level of instant convenience we had decades ago that modern devices are severely lacking. Having to tether your phone to a battery bank while on the go is nowhere near as good as just popping the back cover and replacing the battery.
I had one of those laptops (a PowerBook). Yes, it had two slots that could be used for batteries. But that meant taking out the CD drive. Modern laptops don’t have that anymore so I’m not sure where the room for another battery would come from. The other thing is, it lasted at best 4-5 hours on one battery when doing light work. Its modern counterparts last 10-15 hours on one battery.
The same thing actually happened with phones. But now we literally can’t spend half a minute not looking at them and we also play energy hungry games on them etc. You can still get a phone with replaceable battery though, e.g. Fairphone or Volla.