Every iPhone battery starts as a lithium polymer cell—but that’s only the beginning. Before it can safely power your phone, it has to be programmed, assembled, tested, and inspected. During a visit to one of China’s largest battery factories, I got the chance to build an iPhone battery myself and see just how much engineering goes into something we usually take for granted. From programming the battery management system to quality control testing, here’s what it takes to make a battery that’s safe enough to go inside your phone.
