You know, I had exactly the same problem. I'm a little irritated about it too.
I have several USB devices with batteries, including an iPod shuffle, a Palm Pilot, and a DVD-ROM for my laptop, all that use the USB port to power and charge the batteries. They all use the 5.0V power from the USB to charge and power the device. Thus I also have a couple stand-alone chargers so I can charge them (including a 110V/220V AC charger and an auto charger, both that convert to the 5.0V charge in a standard USB port). Then I just plug them in, and I can charge them without firing up my computer. It's real slick. Plus, the same charger works with multiple devices, so I only have to carry one.
So I had assumed I could use them to charge the RAZR. In fact, many of these third party accessories claim to do the same thing, as they thought the same. In fact, you can use them with all the above devices. Except the RAZR.
Thing is, I can't understand why the RAZR would know any different. The charger that comes with it is 5.0V DC, just like the USB port. In fact, I can even use the RAZR charger to charge my DVD-ROM. (The others use have a different plug so I can't physically charge them without some B-A/female adapter that no one makes.)
Here I thought, finally, a cell phone that uses a standard charger, and not everyone had to be different so they could charge you 1000% over cost for their proprietary cables, and have a million cables, one for each device.
Sadly, Motorola disappointed.
And the idea that because it's a third-party that's it's not up to quality is bump-kiss. As long as they meet the specifications, they're as golden as OEM. It's Motorola that isn't following the standard.