Is there a link for replacement filters? What’s the price like?
Yes, for about $14.99. Here is the link www.megawise.com/f18
How many square feet does it cover?
It covers up to 200 square feet.
Does this help with pet odors? More specifically litter box odor?
This purifier with the H11 HEPA filter can clear out 95% of 0.3-micron airborne contaminants, reduce and absorb smoke & odors via the nano-silver coating and carbon layer. I believe the pet odors and other odors you mentioned can also be eliminated
Does it run on batteries?
No, but the power cable is a USB. so you could always plug it into a portable battery if you need it somewhere you can plug it into an outlet.