[akvadrako]

They are usually shaped to fit in exactly the space available to maximize capacity. Standard cell sizes wastes space.

Besides it's pretty easy to get custom battery pouches made.

[mcny]

Who will make these custom battery pouches for old phones though? Think my old Poco x3 pro, not the iPhone 17. I am sure there are tons of people willing to make batteries for the iPhone 17 but I feel like the interest wanes as the phone gets older?

For older phones, the batteries we buy are likely also old stock left over if we can find some in stock anyway, right?