There was a little flashlight that came with the Les Stroud Engage multitool. Once the worthless whistle was removed from it, it was actually a neat, super-tiny little flashlight. I ran it for maybe a total of an hour run-time or so, and now the batteries are dead.
It runs on four LR621 cells. On Amazon right now, I can get a 20-pack for about $5.50. That means it would cost me $1.10 in batteries every time i wanted new ones in this thing. Which is every hour of run-time.
Orrrrr... I could buy a 55 cent Fauxton, that will run about 2 hours. Mmmmm? Tough one.
I would also like to take a minute to compare that to the flashlight in the Bear Grylls Survival tool pack, called a 'Gerber Tempo'. That one uses a AAA and runs... Well, I don't know. Mine still has the original battery it came with, and probably has 2 or 3 hours of run time on it. It's supposed to get 4 hours from a single AAA. Then, I'll have to pay a whopping... I dunno, $1 for an 8-pack at the dollar store for more batteries. Which, by the way, the batteries are available at the dollar store, or gas station, or anywhere.
I just got a 10-pack of LR621s from ebay for $2. That will give me two... AND A HALF... battery replacements. The flashlight is the smallest functioning flashlight I've ever seen, and just for that novelty feels like it's worth a couple dollars in batteries, but man... disappointing.
EDIT: The LR621 battery is also known by a bunch of other names, like AG1.