really, the best way to find your devices best kernel on battery is to try them out, decide on the one thats best for your device, and for your personal needs and usage. all our devices vary, so do our usages, and so do our needs. anyways..
battery life is determined by your personal usage, your person setup, your personal method of app management, and most importantly battery life is determined by the quality of your personal data/phone signal. everything else, including undervolting, only provides negligible results. thats why no matter what rom you are running, no matter what kernel you are running, no matter if you are using dalvik or ART, there are people that will say that it gives them great battery life while others say it doesnt give them great battery life.