I've done it before but never took an image. But you're asking for proof on something that wouldn't be consistent with other things each time. For example, many things will effect how long the screen can be on such as: signal strength, type of signal (3G, 4G, Wi-Fi), usage while screen on (Browser, YouTube, Texting), screen brightness, calls throughout the day, etc.
My battery life tanked after ICS. I saw some people here advocating a factory reset and I SO did not want to do that, but nothing else worked. So I did it, and reinstalled my apps, and I'm back in business with battery life of 15 hours at 50%, etc.