My backup light is a "Pak-Lite".  It is a couple of LEDs with a switch, mounted on a bit of plastic that snaps onto the top of a 9 volt battery. The 9v battery, along with a little steel wool, is also my emergency fire starter.  The pak-lite can be found at   (You need to Login or Register;  It is small, light, and seems to last forever.  I have had one for several years.  I use it as light in my tent at night to provide a bit of general light.  I just have the basic model, and it seems like the battery lasts forever.