Spring Cleaning and Battery Testing

One other thought for the automated "instant" testers - While this may
indicate the Ah capacity of the battery, is that an accurate
indication of the often asked question "But, how long will it last?"
Literally, does it tell me how many minutes do I have between full
charge and my minimum voltage threshold? There is certainly a
corrolation between Ah capacity and the duration of actual use, but is
there a formula?

Thanks once again, John DeRosa