4R25 as a power source for a mod

Not sure if this has been discussed before, but I find it a little surprising that there aren't more lights around in here using the 4R25 (rectangular 6 volt Zinc Chloride) batterys. I don't know precicely what the runtime on something like that would be, but they're inexpensive (I get them from a garage shop for £2.25 apiece). The flashlight I have has a lamp which is rated to draw 750mA, and has had a couple of hours of use so far, and doesn't seem to have dimmed visibly.

OK, sure, they're pretty bulky, but surely someone who's just looking for sheer power would find that a secondary concern.

I'm no expert on this, am just curious, thought it might be a suitable supply for some future mod.

Zel.