Originally Posted by @rbiter
your statement is a myth. it doesn't improve dramatically but nonetheless it helps. when I undervolt I am more looking for my CPU to stay cooler these add longevity and not letting the battery heat up as much. out of all my undervolted phones, there was a noticeable improvement on my galaxy nexus with battery life and heat. my note3 isn't dramatic, but I do notice my phone rarely gets above warm now. and depending on the bin of your chip, your undervolt can have more desirable effects if you have a great bin. my moto x had a 3 out 4 bin but I never flashed a custom kernel. my HTC one m8 has a bin of 9 out of 16. decent. but the guys who 13 and 15 bins should get great undervolt. undervolting is worth it. adds longevity to the battery itself the less it heats up.
sent from my HTC M8 using hofo app
Pretty sure I mentioned it keeps heat down.
And I could have posted a huge long reply the first time....but "generally", undervolting to improve battery life is barking up the wrong tree. YES it should have minor improvement....but not anywhere near what some people hope when they do it.
At best you may gain a couple total hours and maybe 20, 30 minutes screen time.....if you tweak other kernel settings as well??? Hopefully we can agree on that. And to me, the possible instability from guys pushing the limits is not at all worth those small battery savings.
As far as longevity of the battery.....all I know is my oldest device is 3 years old...and battery life is as good as it was when I got it. But sure, it might help.
Heavy gamers or anyone with heat issues....yes....undervolting will help.
Guys with "bad" battery life.....you will at best go from "bad" to "still pretty bad".