As someone who builds battery systems (yes, I'm "that battery guy" that shows up in HN battery threads) wtallis is correct: full discharges harm modern batterie

As someone who builds battery systems (yes, I'm "that battery guy" that shows up in HN battery threads) wtallis is correct: full discharges harm modern batteries, although every battery protection circuit has a cut-off voltage set to prevent discharging them too far (at which point your phone will turn off.) The practical applications of those two facts, however, are much more nuanced. Ultimately, the biggest killer of batteries is heat. Charging your phone and using it battery-intensively (max brightness/lots of processing stuff) are the biggest heat-causing things that come to mind. Another thing that can happen is heat buildup: you might not be using it very intensively, but if you use it for hours on end the heat can eventually build up and the phone will get hotter over time. It's entirely possible that your method of using your phone actually does cause less stress on the battery. However, this is 100% dependent on what you and your friends do with your phones, before and while they charge, as well as the kind of phone, its charging circuitry and a million other factors. At the end of the day, all I can say is "batteries are basically magic, use less power, and don't let your phone get too hot." The only universal recommendation that will guarantee better battery lifetime - with every battery chemistry - is to draw less current from the battery (on a phone: turn down your brightness, turn off things you're not using, etc etc.)