Comment by PaulKeeble

No manufacturer is testing the batteries life by just charging and discharging them daily for a decade before releasing them. Instead they are using artificial acceleration techniques like getting the battery hot while charging/discharging continuously to simulate a longer lifetime. They can't realistically do anything else to estimate it. But it turns out heat is the big enemy for li-ion batteries and if you can keep them on the cooler side of their range they will last a lot longer.