You realize you can also use a microcontroller to completely shutoff cells so they don’t get used until one dies yeah? There’s multiple tech in these packs now.

Some pieces of equipment allow you to put two batteries in it, so when one is depleted it automatically switches over to other one. Same kinda concept, just done at the cell level.

Think of a battery pack like a backpack, it’s lots of cells in series, to make larger batteries, you make the backpack larger and hookup more cells. A fancy controller can control which individual cells are active. Or even think multiple backpacks, now linked together.