Increased battery life is easily one of the most sought after improvements to a device and often drives intrepid users to root their phones, flash new ROMs, and try out experimental kernels.

Of these modifications, a new kernel is most likely to yield noticeable battery benefits. While the Franco and ElementalX kernels are virtually household names at this point, if increased battery life is your primary concern, you might want to check out the lesser known Hells-Core kernel on the Nexus 5 and Hells Doctor on the Nexus 4.

Hells-Core is developed by Laurent Hess and is available for both the Nexus 4 and 5. A large part of the reason why it is not very well known to the English speaking world is that the bulk of the development documentation for Hells-Core is in German.

Hells Doctor was created by Romain Semanaz and is based Hess’ work, but is optimized for the Nexus 4.

Prerequisites

• Rooted Nexus 4 or 5
• Custom Recovery

Step 1: Download the Kernel

Download the correct kernel for your device and current ROM.

• For the Nexus 4, look here for Hells Doctor (Use the download button on the top center of the page)

• For the Nexus 5, look here for Hells-Core

Again, be sure to download the correct kernel for your ROM. For the Nexus 4, there are standard (AOSP) and CM options available. For the Nexus 5, you have the option between a standard 4.4 kernel and one for MIUI.

Step 2: Reboot into Recovery

Reboot your phone into recovery mode by powering it completely off, then restarting it with the power and volume down buttons pressed.

Using the volume buttons, scroll through the selections until you see Recovery Mode, then select it by pressing the power button to enter the recovery.

Step 3: Flash the Kernel

Once in your custom recovery, select Install and navigate to the kernel update ZIP file that you downloaded in Step 1, then swipe to confirm the flash.

Once the kernel is installed, head to the Wipe menu, clear the Dalvik cache, and reboot your phone.

Step 4: Configure the Kernel

While Hells-Core and Hells Doctor both do a great job of improving battery life right out of the box, they can be easily be modified using the Hellscore Kernel Manager app which can be downloaded from the Play Store for free.

This kernel manager app gives you a huge variety of options to tweak and change, ranging from CPU/GPU settings, undervolting, wake gestures, IO schedulers, and more.

While there are tons of settings to play around with, a good starting point for increasing battery life is the following:

• Change the CPU governor to Intellidemand (or Intelliactive) and reduce the Min. Frequency to the lowest possible setting.
• Change the GPU frequency to 325 MHz
• Change the IO Scheduler to Noop

Be sure to check the Set On Boot box and tap the check mark to apply the settings.

While you may be tempted to play around with different CPU/GPU governors, I/O Schedulers and other settings, you should find that even with minimal modification, the Hells-Core and Hells Doctor kernels noticeably improves your battery life while not sacrificing much in terms of performance.

Give these kernels a shot and let us know how your battery life has improved in the comments below, as well as on our Facebook and Twitter feeds.