Having come from a Samsung Alias, I really have no experience with what to really expect out of any smartphone as far as battery life is concerned, but I have seen a number of screenshots of other users posting their runtimes. If I use the phone sparingly, it's not difficult for me to achieve the advertised runtime of 20 hours with 40% or so to spare - but if I start to seriously use it, I run into trouble, fast.
As the attached screenshots hopefully suggest, I typically get no more than about 2 hours of "screen on" time in any given day. (I try to cease usage by the time I hit 30%.) My typical usage habits include a fair bit of web surfing in Chrome, with a side of texting and text-only Hangouts. Wi-Fi is pretty much always on unless I know I'll be far from a router (hey, I'm on a low-tier data plan), and I though don't use Maps often, I leave the GPS toggled on. My phone is on stock Jellybean 4.1.2 (98.30.1), and is neither rooted nor bootloader unlocked.
(What really makes me worry about this is that the Moto G - a budget phone - reportedly gets SIX hours of screen-on time on one charge. WTH?)
Is this a realistic expectation of the Razr M's battery longevity, or is something, perhaps, amiss?