I have AOKP build 33 with Faux kernel 016b5. This is my first ROM and kernel so I'm not sure what to expect. I've played around with the ROM and I pretty much understand everything, now the kernel, not so sure. One out the reasons I chose to root was better battery performance. After flashing ROM and kernel I've noticed no change (or worse?) in battery life. I've read too much and seen too many screenshots of battery performance to think that the kernel just sucks, so I gave it the benefit of the doubt. I can see the kernel is installed in the "about" section, but other than that, there's no evidence it's actually there. I've also read that you can overclock and undervolt but do far I've found no kernel options allowing me to do so. There is the option to increase Max CPU and decrease min CPU and an option for voltage control which I don't really understand but those options are in the ROM control menu of AOKP. Please enlighten me.
Well, the kernel IS working or your phone would not be... For more detail see here. Now, depending on what kernel you are using, you may have other options surrounding over/under clocking/volting. I'd highly suggest that you avoid custom volting, at least... until you've got a better grasp of what you are doing and spend more time in the thread specific to the kernel you are using. If you do go in and find where to over/under clock, make sure that you do not set to clock on boot until you are 100% certain that the phone is completely stable. Hope that helps! Good luck! I think you may find that people will offer advice on different ROM/Kernel Combos that work well for them, but everyone's mileage varies as far as battery life is concerned because everyone uses their phone differently. Some people update their weather (plus 'x' other cities) every 15 minutes along with 5 email accounts, facebook, twitter, etc.... and some have one location, one or two emails/calendars and no social updates going on. The bottom line will probably be that you will find the more stuff you are running on any ROM/kernel combo will still kill your battery faster than not updating a million things.
One of the reasons that I'm running with Franco's kernel on AOKP is that there's an app for it. The app allows you to update the kernel but also to tweak all the settings - overlooking, undervolting, shutting down cores etc etc
