It's not the store's metric, it's the battery distributor. (Was Exide at the time.)That's fine by me. The store having a metric is fair, as long as the battery at that threshold will actually start the car. The OE specified a battery for my vehicle with some margin for degradation, so that seems reasonable. However, CCA rating is at 0 F. If a battery can't meet 50% of a CCA rating at storefront testing temperatures, that's pretty bad.
The professional Midtronics tester had a little infrared port one pointed at the battery so it could take its temperature and compensate. Not fool proof but the best they had at the time. (2012)