SetCPU is a powerful tool for changing the CPU settings, offers the ability to overclock and/or underclock CPU on a rooted Android phone.
SetCPU also allows you to set up powerful profiles to change the CPU speed under certain conditions, such as when the phone is asleep or charging, when the battery level drops below a certain point, when the phone’s temperature is too high, or during certain times of day.
With SetCPU you can control CPU’s voltage, available to certain devices with custom kernels that support it, to control undervolting to save even more battery. Undervolting is only available for certain kernels (default stock roms does not support such settings).
Download SetCPU v2.3.0 from Google Play store (web link).