I've had a 57 Tbird for about 2 years and never a battery problem. This morning I went to start it and battery is dead. Put a meter on it and read about 8 volts. Now here's the strange part. I went to connect a battery charger, holding the negative cable in one hand not touching anything, connected the positive cable with the other hand and it sparked when making contact with the positive terminal. The charger was not plugged in. What would cause it to spark like that?