Whilst some do you use cigar lighter sockets for charging it's not a good choice and was certainly not designed for such. It's all in the name but over the years became (sadly) accepted as a power source for accessories. The lack of positive security and spring loaded point contact for centre pin do not make for an ideal connection. MMC's current face down location does nothing to improve these facts with a good jolt often parting plug from socket.
Hella/DIN sockets are however designed to power accessories, have a positive pin location and higher current rating. Once you have such there are adaptors available (eBay) to give a couple of USB outlets.
