There isn’t much of a difference between the Motorola Droid Razr and the Motorola Razr MAXX, although we can say that the latter’s battery performance is ten times better than its younger Razr counterpart.
If however, you have the old Motorola Droid Razr but want to get the battery life of the MAXX, you can now do so by taking the battery and the battery door from the Droid Razr MAXX and replace that of the Droid Razr. This has been successfully done by Wardo5757, who is an XDA Senior Member. Now isn’t that enough assurance that he knows exactly what he’s doing?
However, do keep in mind that such method has its dangers and it is your responsibility to do all the necessary research first before attempting this. Failure to do so can cause serious damage to your unit, battery, and its battery door because first, the battery door is not that easy to open plus the battery is tightly sealed in. Although both parts are removable, this can only be done if you have the right tools and the courage to do it.
After successfully removing the guts from your Razr MAXX, you can then easily transplant the battery door and the battery itself from the MAXX to your Droid Razr. If there’s any downside to this process, it would be the small gap between the battery cover and the SIM card door. Although this does not affect the phone’s performance at all, do keep in mind that it will affect your Razr’s resistance to dirt and water.