Well I dug up the link I was referring to above about a home made power packup system. Regretably I was remembering incorrectly and it wasn't as cheap as I had thought I read. But, for those with a large number of animals it would still be well worth looking into and cheaper for larger operations to prevent power failure. Take a look at the link if you wish, otherwise I stand by my thoughts on a normal UPS unit. I will probably start looking online at some and around local stores to see what I can find. For just a few animals a fairly inexpensive UPS unit I would think could power their heatpads so they still have a constant source of heat.
Link: http://www.dansdata.com/diyups.htm