I don't think whatever issue you've been experiencing will tied to waiting for the battery or the Android operating system on your phone to 'settle in'. A Factory Reset does not do anything to the operating system, it only does one thing -- it wipe the /data partition clean. The /data partition is where all your data and the apps you've installed reside. The operating system is spread out in different, separate partitions reserved only for the operating system. So your operating system, and its links to the battery as the same before the Factory Reset and after. It's only that your data has been deleted (and if you're lucky, maybe some app that was draining off to much or was in some way messing with the power management.) So it just doesn't seem like there's a reason to allow for a 'settling in' period, and yes the phrase itself, "Factory Reset" is definitely a bit of a misnomer. If you do want to go as far as replacing the operating system, that requires you to flash a stock ROM, an entirely process than a Factory Reset..