Well Ed, I finally had a clear head to attempt this.
The short answer, in my opinion, there is no short answer, it depends on several factors including battery chemistry, discharge rate, ambient temperate, and how long and under what conditions they were stored, to name a few.
The best general solution is to know where you are buying the batteries from and your past experience with them.
Major shows and productions often get their batteries directly from the factory or a known distributor, that guarantees freshness.
That said I would not trust most retail outlets (Walgreens, Target, Walmart, Fry's etc.)without having several random destructive load tests runs.
I personally buy my batteries for critical applications at one of the two electronic stores in town, that I have dealt with over the years, questioning their storage and arrival dates from where of the batteries I am considering.
In my personal experience that is the only way to have a reasonable chance of freshness and even that is not 100%.
If you wish to read primers on the subject you can check out these links.
The above is oversimplified and many would say overly cautious.
Each to their own beliefs.
Trust this helps.
https://www.powerstream.com/9V-Alkaline-tests.htm
https://batteryuniversity.com/
https://www.medicbatteries.com/battery-information-center.html