Franco's Kernel is brilliant.
That being said, it really depends what you do to the device that'll end up saving you battery. Underclocking, undervolting, capping the suspend frequency and sleep inducing are all good ways of conserving battery.
Underclocking
This is really just stopping your device at a maximum frequency, also you can limit the number of cores that go online by adjusting the high load threshold (you can do all this from the Franco app). For example if you're viewing a video from local storage you can cap the frequency at 800mhz (and at 2 cores by setting the high load threshold to a high number), instead of letting your N4 run all the way up to 1.5ghz (theoretically it'll draw the amount of processing power it requires but this is just a way to be safe
).
Undervolting
The name says it all; supplying less power to the processor. Manufacturers tend to set higher power inputs to the processor to ensure fluidity, you can change that to improve battery life. I've undervolted my 384mhz to 725mV, and my 1512mhz to 1025mV and it runs fine. The battery life is marginally better.
Capping the Suspend frequency
Setting a maximum processor speed when the screen is off. You can also do this from the Franco app, though setting a low number would result in noticeable delay in receiving push notifications. It works well if you listen to music a lot, or don't really use your phone to stay online all the time. (Mine is set to 594mhz and I receive pushes without a problem)
Sleep Inducing
Paranoid Android (and some other ROMs) allow you to add a "Go To Sleep" button on your Quick Toggles pull-down, this puts the phone directly to deep sleep without the usual winding down period.
Hope this helped!