as days pass by

Laptop life has been constant-ish, for years. You can get three or four hours out of a decent modern laptop; it used to be one or two, but it’s all of that order. Not enough for a full day without recharging. Do modern laptops use more power? They certainly do more stuff—CF readers, CD readers, better screens. Could you take a battery from a brand new laptop and use it to power your old P200 laptop for eight hours?
Well, of course you couldn’t, because they’re all different shapes. This is (charitably) because laptop designers need to craft everything specifically for each new model so that it all fits together as tightly as possible, to minimise size, or (uncharitably) so that you have to buy a new battery every time you buy a new laptop. But ignore that; imagine the shape and connections issues don’t come into it. Does a modern battery produce more power from the same size of battery? I imagine they do; technology marches on, after all. So if I took the battery from a brand new laptop and I put it in my old Toshiba Tecra 520CDT, which is a P166, would it run for eight hours? Or ten hours? Or 24 hours? It would be great if it would. Who knows about battery stuff?