I just upgraded my phone from the original Motorola Droid to the Galaxy Nexus. Both phones use the same micro USB port. Is there any reason I cannot use my Droid's car charger with the Nexus?
It should work fine -- Micro-USB is Micro-USB. The only possible caveat is the phone and charger may not negotiate high speed charging. However, that's unlikely.
My wife and I have shared wall and car chargers between her old Droid, current Droid X, and my Incredible without any problems.
It turns out that the car charger I bought for my Moto Droid is unable to charge the Galaxy Nexus. It just does...nothing.
It could be an issue with the actual car socket. Ensure that the fuse is intact, and that the socket is working fine.