This is for rooted users only.

We all want to squeeze every last little bit of juice out of our devices that we can, and if you happen to have a rooted HTC EVO 4G running an AOSP kernel (such as the one that ships with CyanogenMod), then XDA member -viperboy- just made your life a little bit better. Thanks to him, there is now an easy to way to undervolt your kernel, by way of four flashable .zip files.

Generally speaking, AOSP kernels are volted to support several different devices, so it stands to reason that some devices could handle lower voltages. With that thought in mind, -viperboy- set out to create scripts that could lower both the minimum and maximum voltages of the kernel, without compromising stability. The end result was four incremental scripts ranging from -25mV to -100mV (that's the undervolt amount), which should provide a working solution for everyone.

-Viperboy- noted that while everyone should be able to use the -25mV or -50mV scripts without an issue, the -75mV and -100mV scripts are fairly extreme and may send your device into boot loops. Fortunately, he also created a reset script which sets all voltage values back to stock. If you plan on giving this a shot, make sure you download the reset scrip and put it on your SD card along with the other scripts, just in case you encounter any problems.

As always, it's recommended that you make a backup before attempting any drastic mods and if you have any problems, hit the source thread for more info.

Source: XDA