Direct Connect Solar Panels to 12v Chargers (for misc electronics)
The car charger is most likely a small switched mode power supply.

This should be fine running from any voltage (assuming a 5v output) of say 7v up to 50v+ (check the chip to be sure of the upper limit).

I am currently working with the MAX5035 family of chips which run from 7.5VDC (or 15VDC for the 12V version) up to 74VDC to give 3.3V, 5V or 12V.