could be good for a car too if you drive a lot.
You could just mod a car charger for a cell phone for use in a car while driving. You would probly get somewhere between 4 and 5 volts from it.
Or you could just buy an ipod car charger adapter that would give you one or two usb ports and use a usb passthrough with it.
I know the new Hyundi Tuscan comes with a usb port already for ipods, some aftermarket car stereos have usb ports on them as well for thumbdrives with music on them.
I couldnt ever see myself using needing a 6v lantern battery. I camp but I would just use a solar charger with a usb port on it.
P.S
Does any one know when new users are allowed to create their own threads? I love to mod everything I buy and I am sure I could post a few helpful threads.