Batteries is one of those things we go through in our classrooms like water. Sometimes our districts/agencies/schools order them from a catalog like WB Mason, Staples or Office Max; sometimes we get to pick the catalog we order them from and sometimes we have to pay cash out of pocket (a lot more often than I like).
Consumer Reports tested and rated AA batteries and found that the best way to buy batteries is purpose specific. So if you are buying batteries for your digital camera or video camera (or other intensive output devices) go with the Energizer e2 Lithiums, which cost more at the outset but save you in the end. Of course they don't say what to do if you are buying for the assistive technology in our classrooms, but it sounds like you should consider Panasonic Digital Extreme, Rayovac, and Kirkland Signature (from Costco only) alkalines. Stay away from CVS brand though. Intensive search engine browsing could not find any reliable info on the best 9-V batteries for our Big Macs and Step-by Steps.
Good luck finding a tiny screw driver to open those battery doors!