A great source for battery-operated items to help in the
event of a power outage is mail order sporting goods catalogues,
especially the fishing and boating ones. Many of the products are for use
in live-wells or pumps and are quite applicable to aquarium use
and usually cheaper than the aquarium industry equivalent.
Cabela's has battery operated air pumps (for use in live wells)
and a battery operated immersible pump that runs on 2 d-cells.
I have used the pump quite often, it is great for water changes,
and probably could keep a filter system running for quite some time.
I don't know how well the 'lifting' capability is (i think the
proper term is 'head'), put it would circulate water in a tank
very well. You might have to get Cabela's Marine/Boating catalogue
for the listing (it was very reasonably priced).
I am constantly on the lookout for products from other industries
that have applications for aquariums. It seems a product developed
for a particular industry will be overpriced, but a similar product
somewhere else will be dirt cheap (I suppose the equivalent would
be the discussion of T-8/T-12 lights versus aquarium specific lights).
Hope this helps.
Peter J. Kinslow
pkinslow at denadm_ms.ch2m.com