Why don't they make AA / AAA / 9v batteries that don't die gradually?

In our phones, the battery provides full operating capacity, until the battery gets too low at which point it shuts off. It's either on, or off, not somewhat-on. Yet AA, AAA, 9V etc. still all gradually lose power towards the end of their life, causing the device to lose functionality gradually. Why... show more In our phones, the battery provides full operating capacity, until the battery gets too low at which point it shuts off. It's either on, or off, not somewhat-on.

Yet AA, AAA, 9V etc. still all gradually lose power towards the end of their life, causing the device to lose functionality gradually.

Why can't this be done with regular batteries, as it is in phones? thanks.
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