If you are using a meter to check your battery and it is showing good it may be a bad connection somewhere in the circuit. Have the terminals and the battery posts cleaned, if it still doesn't start try jumping the battery. If that makes the car turn over chances are it is the battery no matter what the meter says.

Any store that sells new batteries other than Auto Zone will give your battery a free 15 second load test to see what the reserve *amperage capacity is. Amperage spins starter motors not voltage.

Car batteries, and even flashlight batteries can "read" good, in other words show the correct voltage, but be bad when a load is placed on them. Test it with a load, and that will tell you for sure.

Don't know what you are using to "read" the battery, but if you have a volt meter, then a fully charged car battery should read somewhere around 12.5 to 13.5 volts.

Does it spin the engine fast when you operate the starter? A good battery turns the engine over rapidly with no hesitation.

Take it to an auto parts store and have them check it. Then you will know if it is bad or not.