Was it really necessary for Apple to slow down old iPhones?

Apple yesterday confirmed that a long-held and controversial conspiracy theory actually contains some truth. The company says that, starting last year, it started slowing down older iPhones with lower-capacity batteries, mainly to prevent accidental shutdowns. The news set off a wide-ranging debate about smartphone reusability and longevity. But why does Apple need to do this in the first place?
First off, think of a battery like a system of pipes with water, says Marca Doeff, a battery expert a