Whether you want to run your battery down to see how fast it can charge, or because you're playing a cruel joke on your friend with his phone, sapping a battery of its charge is fairly easy and fast. Some phones, such as smartphones, eat up more of a battery charge than others. Even if you have a standard cell phone, there are a few settings you can change and applications you can run to drain the battery.
Access the "Settings" menu and select the "Display settings." Turn the screen "Brightness" and screen "Timeout" to maximum. Screen timeout is the amount of time that a screen will stay on before it turns off due to inactivity.
Open a GPS application. If the phone has a GPS application on it, starting the GPS will drain the battery faster than anything else.
Open the Internet browser. If the phone doesn't have a GPS but comes with an Internet browser, you can also browse the Internet. The battery won't last more than a few hours at full charge.
Play games. Games are resource hogs and take a lot of power from your phone, sapping it of its charge.
Launch multiple applications at one time. If the phone is a smartphone, then it may have the capability to run more than one application at a time. Multiple applications mean more resources, which means the battery will drain faster.
Do not launch the Internet browser if the phone does not have a data plan, as you will incur data charges.