I also had a "run forever survival light" in mind when I did some research a year or two back and came across Wayne's (Elektrolumens) Blaster 1D.
I bought just one from him but wish I had bought a couple more.
It'll run forever on one D-Cell battery, and it's plenty bright for normal use in the kind of emergency situations I had in mind.
It's more like 60 lumens as opposed to just 5 lumens desired in the OP, but the Blaster will still run for 3 days straight on one D cell, and I use it also as a room lamp during a power outage. I tail stand it under one of my table lamps and throw the light up into the lamp shade. That diffuses the light from the Blaster and it becomes a very good backup for when the lights go out.
Using rechargables for a "survival" light doesn't make much sense because it's quite possible that you won't be able to recharge them anyway if the power is out.
Scroll down the link below and you can see what the Blaster 1D looks like.
I'm seeing a preference for 123's, but there is nothing like a D Cell if you want a runtime that you won't believe, and don't forget the very easy availability of D cells anywhere.
For the purpose stated in the OP, I would highly recommend seeing if you can talk Wayne out of another of his Blaster 1D's or a Blaster Jr.
http://www.cpfmarketplace.com/mp/showthread.php?t=129788&page=3