First, out of honesty- the biggest reason I chose the Rezound over the Razr is that I loved the Rezound's screen and found the Razr's screen to be incredibly, awfully hideous- worse than the original Droid or iPhone. I still can't understand how anyone with decent vision can like the Razr screen.
But putting that aside, I'm not convinced of arguments in favor of the Razr Maxx's battery life over the Rezound, at least for a typical user. Here's why:
1. The Razr battery is non-replaceable.
2. Every battery degrades over time and through use, including the Razr Maxx.
3. Most people don't want to replace their phone every six months or year- this is a two year purchase for most people, and even longer for some.
4. For the Rezound, you can easily buy a new battery when your old battery gets bad. For the Razr Maxx, you can't.
5. The Rezound extended battery is almost as powerful as the Maxx's, and when it degrades, you can buy a new one.
6. You can also simply carry around a spare, charged standard Rezound battery. It's amazing how small this battery is- you could easily put it in your wallet and never notice it's there. Then, when your current battery runs out (which, for most people, if it happens at all will be late in the day), you can easily swap batteries. Two standard Rezound batteries have about the same charge as the unremovable Maxx battery. And when they get bad, you can replace them.
7. If my suggestions for the Rezound sound expensive- the current price of the Rezound is so much lower that you'd still be saving money even after buying extra batteries.
I'm not saying that it isn't nice having a huge battery in a smaller phone, and swapping batteries or having the larger extended battery case might not work for some people. But if your highest priority is battery life, and you plan to keep the phone for longer than a year, it seems like the Rezound is the better choice.