The biggest battery hog in a device? Typically, the screen. Turn down the brightness level when you can. Some new phones, such as Samsung’s Galaxy S5, have settings that turn the display to a black-and-white mode to consume less power. If you need even more juice, shut off wireless connections such as Bluetooth and Wi-Fi.
Batteries are like you or I: they don’t like working in extreme conditions. Don’t place devices in the sun or leave them locked in a car during the summer. If you do, the device might refuse to function, saying it needs to rest and cool off before you can get back to reading the latest gossip about the British royals.
It used to be you had to discharge your battery all the way every time you used it. That went away in the 1990s when we started using lithium-ion. Even so, it’s still a good idea to exercise a battery once a month: run it until the device turns off, and then charge it until full. That will keep it charging up to capacity.