Riddle Me This

This is real random: I bought Serena a headlamp for her big Peace Corps adventure. So as not to leave her with the hardware without energy (apparently the batteries in Swaziland blow) I was going to buy her batteries, but came to find out they were really expensive: $8 for two at Bi-Mart (for you East Coasters, Bi-Mart is a big box store like Wal-Mart but employee owned). I started poking around and found a pack of two for $3 at Office Max. Neither was on sale, both were name brand (Energizer vs Duracell). Wtf? Any ideas?