Why pay for diagnosis [of a battery] ?
Our local auto parts stores (Pep Boys, AutoZone) test batteries for FREE
even if we don't buy the battery from them.
In essence, they will test the battery voltage before the load test; put a huge load on it for a short time, then test the voltage again. They will even give you a printout of the report.
Also, if needed, they will test the current being put our (with an ammeter) as well, while the car is running.
If you already knew all of the above, *ignore this message* :-)