Running An Air Purifier on Batteries

Running an air purifier on a battery could be really useful in an emergency that combined a biological or nuclear threat with a power outage. Getting one that can run on 12V DC and attaching it to a LiFePO4 battery is about $188 (plus $164 for the purifier) for something that will give you 141 CFM for over a week. I've been thinking about DIY biohardening, primarily to reduce risks from environment-to-human threats, and a lot of what's out there assumes the power grid stays up. This doesn't seem...