B&D trips breaker but runs on 12v battery

I have a B&D 875 that trips the breaker when I pull the handle up. Thinking the motor was bad, I hooked up a 12 volt car battery directly to the motor and the motor turned over real slow but no smoke or smell. Does the rectifier actuially put out 110v dc to the motor? It's hard to tell when it trips the breaker. I hear a noise in the handle switch when it trips the breaker. I''m going to try a 48v battery pack from a scooter. I heard someone mention an AC blade break function. How does that work?

B&D trips breaker but runs on 12v battery