Bought a few 4pk of Powermax AA batteries at Fry's for .39/pack a few months ago. Batteries have an expiration date printed on the battery of June 2017.
I've been using them mostly for an radio controlled F1 car (6xAA) and a radio controlled coaxial helicopter (also 6xAA). I also put 2xAA in a black MiniMag (non-LED), and another 2xAA in a silver MiniMag with NiteIze 1-watt LED upgrade II (LRB-1W). They were all installed in their devices around second week of May 2012. The silver MiniMag sees the most use, at least once a day for a few minutes at a time when I'm taking apart or putting together things like working on a car or computer or household maintenance.
The silver MiniMag stopped working today and when I pulled the batteries out, the bottom one had leaked, and top one had white powdery stuff on the positive end. I checked the other devices and those batteries are fine.
I'm sure if I used a name brand like Energizer or Duracell, this wouldn't have happened so soon. Cheap isn't always good. =)