The USB outlets have been known to fail. Either replace it or change it out for a robust 12v outlet and use a USB adapter. FYI: The USB outlets draw phantom power.
"Phantom" power is the various drain of the battery that can't be shut off. Like the gas monitor, and the TV/Radios. The only way to stop these things from using power is to shut off the battery entirely with the battery switch, pulling the battery fuse, etc. Here is a thread that discusses the replacement of the USB…