Its either huge resistance, or huge current;
or at this point both.
One high current situation with is recharging the battery when the alternator is generating power above 15 Volts. Another is using the driving to recharge a very low battery
A high current situation from the battery is a short to ground.
Since its badly damaged, there really is no choice. it needs to be removed. Whether you replace it or rewire the system for a voltmeter is up to you.
I would not rewire it as MAD recommends.