Measure it with a voltmeter.
There is a wide variety of pricing for a 12 volt battery. The overall wattage of the battery will determine overall cost. Typically they will cost anywhere from $100-$400 for a new battery.
Charge it with a 12 volt battery charger.
No
12 volt
No, a 12 volt charger will overcharge a 8 volt battery and destroy it.
The battery is a 12 volt.
No
Yes, a 12 volt battery will be damaged if charged with a 24 volt charger.
If you are asking the question, can you charge a 6 volt battery with a 12 volt charger, the answer is no.
No, the battery is DC not AC.
A 12 volt battery charger is designed to charge 12 volt batteries.The answer to the Related Question explains how any battery charger works.
A 12 volt automotive battery has six cells.