[Samsung Epic 4G Touch] iniz94:
51% kernel is high, yes. See if other people have the same percentage with that kernel. If not, then maybe try a different kernel. agat's or sleshepic's kernels are also good and built from source. Btw, I wouldn't advise doing the Developer Options setting change to close all activities. That setting isn't meant for ordinary use and severely limits your multitasking abilities. "Closing apps" also has a minimal effect because of the way Linux deals with RAM. It turns out that opening and closing apps takes away more battery than keeping one running in the background.

If your battery isn't good, diagnose why with the following apps:

Betterbatterystats - Download this app and check your "Partial Wakelocks". Basically this checks what apps are waking your phone up when it's sleeping.

CPU Spy - This allows you to easily see how much time your phone has spent in each state. You get really bad battery life if your phone idles on 200 Mhz instead of Deep Sleeping. Your phone should be on Deep Sleep when the screen is off, or else your idle battery drain will be fast.

Other ways to save battery life:

Tweaking system settings

Get SetCPU/Tegrak/Voltage Control/Any other CPU Settings app and undervolt each of your processor states to -50 mV. By stock your phone's states come "overvolted" and you can conserve battery without loosing performance if you slightly tweak them. Don't go too low or your phone may get unstable and crash.

Use those same apps to underclock or set profiles to underclock under certain circumstances

Use those same apps to change your governor. Read up on different governors and how they scale your processor when needed. Here is a link that explains different governors - http://xdaforums.com/showthread.php?t=1369817 . Usually "conservative" and "SmartassV2" and "Lulzactive" are pretty good with battery life. It all depends on how much performance you are willing to give up for low battery life.

Use those same apps to change your I/O scheduler. The scheduler, in simple terms, basically describes in what order apps will run, which will be prioritized, etc. The "SIO" scheduler is probably the best balanced one. "Deadline" I believe saves more battery life but maybe slow you down a little.

Apply tweaks that do it for you

In the general section of our forums, a developer named PhAkEer has posted some tweaks. His "dietpill" battery ones are really good for keeping your phone fast but saving battery life. If you have these tweaks though, they automatically choose a governor and I/O scheduler so manually changing them will only interfere if you decide to do this.

Change simple unneeded settings

Another reminder is that simple things can save you a lot of battery life. Turn off haptic feedback. Take off pulse light notifications (there are reports that these wake up your phone from Deep Sleep and put the processor back into the 200 Mhz state... thus taking away battery life). Turn off 3G when not needed (3G and 4G are huge drainers). Set WiFi to turn off when your screen is off. There is a ton of other stuff you can do.

Well I hope this long post helps you in your quest to find better battery life. Good luck