A lot of people take it for granted that a laptop can be unplugged and used for a couple of hours without being plugged into a laptop ac adapter but this is only possible because there have been some enormous leaps in battery technology and the near future may well bring some even greater ones again.
The first ever portable computers didn’t have any batteries at all and were plugged directly into the mains. These were called “luggables” and instead of the familiar flat LCD or TFT screens we are so used to now, they had miniature cathode ray tubes in their deep cases and proper floppy disk drives built into them. Some people rigged these early machines (with names like the Osborne 1 and the British made Wren Executive) up to work from car batteries, and the very earliest of these machines were found in Emergency vehicles potentially making them the first portable machines, although in this case the first ever laptop chargers happened to have wheels and an engine.
Apple’s first portable machine was the now very rare Macintosh Portable and in a sense, this was one of the first laptops, you could balance it on a lap at least. This had the now familiar flat screen but in common with our earlier four wheeled laptop chargers, the power source of this machine was an internal lead acid battery. The machine required so much power that the ac adapter couldn’t supply it all unless the battery was in there too.
It did, however run for an hour or more on a full charge.Later portable machines started to demand a lot less power and so were able to use the much more familiar sealed Nickel Cadmium and later on Lithium Ion cells that are in modern machines. Thankfully, laptop ac adapters no longer need to weigh a few tonnes and have their own wheels.