is this a battery problem

the battery reads 12.7 volts when you try to start the car it drops down to 6.5 volts. I jumped the car to get it started the battery then reads 13.7 volts. I took off the belt and the pulleys all spin free I also wire brushed the wire connectors and the battery connectors. Is this a sign of a bad battery.

Your battery shouldnt drop voltage like that.
the voltage should be over 13.5 when you start it maybe a 1 v drop. I would slow charge and recheck or take it to a shop / parts house and most will test for lil or No $. But I would say time to buy a battery.