Look at the manufacture date on any batteries you buy. Often I find duracells at QD stores or even the 99p store. But upon inspection the date is either 1995, or (in 99p stores) the date is blacked out!
So if I brought those duracells, then compared them to ikea's cheapests, yet more recently made batteries, then they would be outperformed.
Dunno how easy that is to follow, but its very important when buying batteries to realize there are very few ways to save money other than buying the right ones first.