Battery packs typically use 18650 Lithium cells which are a bit bigger than AA sized. You can easily replace them in older battery packs (and there are many tut

Battery packs typically use 18650 Lithium cells which are a bit bigger than AA sized. You can easily replace them in older battery packs (and there are many tutorials online on how to do so) but newer laptops have circuitry inside which tracks the number of charge cycles and disables the battery regardless of if it has new cells.