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How to make your cell phone battery last longer
Turn the phone off.
Only do this if it's going to be for several hours; turning a phone on/off actually uses a massive amount of power itself. This will probably be the most effective and simple way of conserving your battery's power.
Why? This will help conserve energy and also charge your phone. If you don't plan on answering the phone while you're sleeping or after business hours, just turn it off.