You could make a dedicated charging cord to go between the cigar socket and the phone/GPS by simply opening up the plug which goes into the cigar socket and bypass the electronics which normally step the voltage down to 6 volts from 12 volts, or just cut off the step down plug and swap in a regular plug devoid of electronics.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission