I have a multimeter and tested my 4 & 1/2 year old car battery and the reading was 13.7. When I went to Autozone, it said "bad" I replaced it under warranty.
Can anyone suggest what so special this Battery Tester they will that checked the battery was bad?

 

Yeah it's called a battery load tester

 

What he means by that is:

A battery load tester measures the CCA (cold cranking amps) the battery has. Yours failed because it had a low number, deeming it bad.

Battery voltage doesn't necessarily mean the battery is good, although it is usually an indicator of bad health if the voltage slowly drops while unhooked from the positive and negative terminals.

 

U can have bad cell but still read proper voltage with a meter. You need to apply a load to test it.

If u have a battery with a bad cell it may start fine some days and need a jump start at other random times.

 

Is there anyway to test the CCA with multimeter? so the realistic some sites say using the multimeter on car battery is not correct then...

 

No, you have to use a battery load tester.

 

interesting I learned something new today..