There are a lot of misconceptions about rechargeable lithium-based batteries like those in MacBooks, iPads and iPhones. Some people suggest running devices until the batteries are drained fully, while others believe that doing so repeatedly will age batteries prematurely.
Thankfully, Apple has published a good bit of information about caring for rechargeable batteries:
That’s a lot of links, so let’s hit the high points:
Leaving a device plugged in continuously will damage the battery over time. For example, if a notebook is plugged in on a desk all the time, Apple recommends you run the battery all the way down at least once a month. The same goes for iPads and iPhones, though, too.
If you don’t plan on using a device for several months, Apple recommends that you store the battery with a 50% charge in a cool, dry place.
The sun and heat are big enemies when it comes to portable devices like the iPhone. According to Apple, the iPhone works best from 32° to 95° F (0° to 35° C).
These three tips can be helpful in caring for a battery, but just like most things, they will wear out over time. When that happens, Apple offers affordable service options to replace them.