In case you have a device that can only be charged using a computer, here might be a solution for your problem!
My Sony eReader is pretty good at battery power because of it's special display. But when the battery runs out, I'm screwed...
Using a standard USB-charger simply won't work. Maybe you're experiencing the same problem with any other of your devices.
Why won't it charge? Because the device waits for a data connection before accepting power from a USB source - it wants to be plugged into a computer!
Here is what to do without having your computer turned on all the time:
Look around you, which other computing devices do you have? Maybe your router has a free USB-port that is working with the device.
I finally found a Wireless LAN repeater I'm using in my house, which does the job very well.
Mission accomplished: It is charging!