The Android Source has discovered that both the DROID RAZR and the DROID RAZR MAXX are running on identical ROM. What this means is that in future if you get an updated ROM for either of the devices, you can easily flash it to the other one without any modifications.
As is usually the case with these things, there could be some risk involved but as was observed by the people at The Android Source by flashing the DROID RAZR MAXX with a DROID RAZR ROM, things seem pretty straightforward in this case.
I think Ill grab a MAXX since it has bigger battery
It's not exactly the same, it's thicker. Both modles are sold side by side by Verizon. Some will prefer the sleek 7.1mm model, others the 8.99mm model with bigger battery. Rumors of the RAZR MAXX were well-known, even before the RAZR hit ...
But how will the software differentiate between the battery differences and convert it to the right percentage?