1. Turn Off Features You Don't Use, Especially: Bluetooth, Wi-Fi, and GPS
Bluetooth, Wi-Fi, and GPS are some of the biggest battery killers on cell phones, because they are constantly looking for possible connections, networks, or information. Turn off these features (look in your phone's settings) except when you need them to save power. Some phones--for example, Android smartphones, have widgets that offer toggles to quickly turn these features on or off so you can switch on Bluetooth when you're in the car for hands-free driving or GPS navigation and then turn it off to save your phone's battery life.
2. Turn on Wi-Fi When You Can Connect to a Wi-Fi NetworkHaving Wi-Fi on drains your battery--if you're not using it. But if you're on a wireless network, it's much more power-efficient to use Wi-Fi than to use cellular data, so switch to Wi-Fi instead of 3G or 4G when you can, to save your phone's battery life. (E.g., when you're at your house, use Wi-Fi but when you aren't near any Wi-Fi networks, turn Wi-Fi off to keep your phone running longer.)
3. Adjust Your Display Screen Brightness and Screen Timeout
As with laptops and TVs, the screen on your cell phone drains a lot of its battery life. Your phone probably auto-adjusts its brightness level, but if your battery starts dipping to levels that make you anxious, you can adjust the screen brightness even lower to conserve more battery life. If you like, you can go to your phone's display settings and set the brightness to as low as you are comfortable with. The lower the better for your phone's battery.
Another setting to look at is the screen timeout. That's the setting for when your phone's screen automatically goes to sleep (1 minute, for example or 15 seconds after not getting any input from you). The lower the timeframe, the better the battery life. Adjust to your level of patience.
4. Turn Off Push Notifications and Data-FetchingOne of the conveniences of modern technology is having everything delivered to us instantly, as they happen. Emails, news, the weather, celebrity tweets--we are constantly being updated. Besides being bad for our sanity, the constant data checking keeps our phones from lasting very long. Adjust your data-fetching intervals and push notifications in your phone's settings and in individual apps themselves (news apps, for example, and social apps are notorious for constantly checking in the background for new information. Set those to checking manually or hourly if you must). If you don't need to know the second every email comes in, changing your email push notifications to manual can make a huge difference in your phone's battery life.
5. Don't Waste Battery Life Searching for a SignalYour poor phone is dying and it's trying to find a signal. If you're in an area with a weak 4G signal, turn the 4G off and go with 3G to extend the battery life. If there's no cellular coverage at all, turn cellular data off altogether by going into Airplane mode (look in your phone's settings). Airplane mode will turn the cellular and data radio off but leave Wi-Fi access on, for most devices.
6. Buy Apps Instead of the Free, Ad-Supported Android VersionsIf battery life is really important to you and you're an Android smartphone owner, shelling out a couple of bucks for apps you use may be worth it, since research suggests free, ad-supported apps drain battery life. In one case, 75% of an app's energy consumption was used just to power the ads! (Yes, even in the case of beloved Angry Birds, only 20% of the app's energy use may go to actual gameplay.)
7. Keep Your Phone Cool
Heat is the enemy of all batteries, whether your phone's battery or your laptop's. You might be able to eke out a bit more life out of your phone if you take it out of a hot case or your pocket, don't leave it overheating in a hot car, and can manage to find other ways to keep it cool.
Of course, as a last resort, turning your phone off when not in use can also cool it down and conserve the battery.