minimal overnight voltage conversion

Hi all,

I have a cabin style situation.  All high loads run off the 24 v system but i have a couple panels that go through a midnite solar unit that runs small loads.  This was against other advice but i wanted both a 12 and a 24 v system separate for different needs.  Anyway, while I am sleeping, I want the small 12v system to run some simple things like alarm clocks and low watt fans.  These have been selected and purchased to use a power source of 5v dc - the same as most phone and usb devices.  In my experience, using an inverter for something like this is over the top and draining.  Anyone know of a device that will provide the 5v dc from 12 v batteries without draining them more than necessary? PS  I turn off ALL inverters when not in use.