This is a really good question that I don't think enough people ask honestly. I learned about checking manufacture dates the hard way after a battery I bought underperformed almost immediately, only realized later it had probably been sitting around for months. There's usually a date code stamped somewhere on top or side of the case, sometimes in a letter plus number format representing month and year. If a shop seems hesitant or unsure when you ask about it, that alone tells you something about how seriously they handle inventory.