Anyone used something like this:
I have the extended battery and it would be nice to have the regular battery charged up for those extended days away from an AC outlet. I had the one from Motorola for my OG Droid and while it took 3 or 4 different battery sizes, it wasn't compatible with the larger size of the battery on the D3.
In theory this should work okay, safer if you force a slower charge over USB if you are worried.
I just went ahead and bought it, for $5, not a huge investment to test it out. I'll report how it is if noone else does before me.