I use 12 volts at the desk. I have run #2 welding cable back there with a 100 amp fuse on each line. Yes it is overkill for charging a phone, but works well with my ham radio which takes 20 amps when I transmit.
There is one 12 volt cig lighter over the desk on our 3055. With no load on it there is about a .3 volt drop from the batteries.