I have a 2003 Mitsubishi Diamante, and I keep two battery boosters in the car "just in case".
My son recently bought a car that had problems starting. He has used both my boosters on his car and claims they are now both broken. He had also, a few times, switched out and used my battery, and now my car won't start.
When the problem started, I was able to charge the "broken" boosters and even though my car would not start on its own, I could at least start it with a booster.
This morning, I went out to the car and saw that he had put a battery charger with missing clamps on my battery. Only the black wires (where the clamp belongs) were connected to the car -- the red side was loose. The charger was blinking zeros and it sparked when I tried to remove the black side wires, so I unplugged it.
At that point, I got my fully charged booster and connected it, red then black, and it instantly drained from 13.3 down to 6.4. The car wouldn't start. I tried again with the other fully charged booster and the same thing happened.
Have my boosters or battery been damaged somehow? Can I fix them?
I know the way he had it connected this morning was wrong, but I can't find any solid info to explain it. I've asked many people why the red cable must be connected before the black, and why it can do damage to your car and battery if this isn't done properly.