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’ve got an old Motorola AMPS phone around somewhere that has a charging cradle that will fit either the whole phone or the battery on its own. Most commercial two way radios still work like that, I wish they would still make phones like that too.
The dual laptop batteries are handy too. I’ve got a Thinkpad T480 and it can hot swap the external battery. The high capacity battery lasts so long that you rarely need to swap it, but if you use the slim batteries, you will need a couple to get through a whole day. Unfortunately, that’s the last Thinkpad model that can hot swap batteries.