Absolute Ayush

Your phone says 80%. You plug it in. Nothing dramatic happens. No smoke. No warning. No little red icon saying Congratulations, you have just aged your battery. You unplug it at 100%. A few hours later, you're at 40%. You charge again. Normal life. Except there is a strange question hiding underneath all of this: What, exactly, is happening inside the battery every time you do that? Most of us imagine a battery as something like a tank. At 0%, the tank is empty. At 100%, it's full. Charge it, and you fill it up. Use it, and you empty it. It sounds reasonable. It is also a surprisingly poor mental model. Because a lithium-ion battery isn't really storing energy the way a tank stores water. It's doing chemistry. And once you see what that chemistry is doing, battery advice starts getting weird. Why can 10% → 80% be better for the battery than 30% → 100% , even though you're using almost exactly the same amount of battery? Why might repeatedly cycling 80% → 100% be w...