# How Does A Dead Car Battery Charge?

Under the typical setup, the jumper cables are connected to the positive terminal on the dead battery, the positive terminal on the good battery, the negative terminal on the good battery, and un-connected metal on the dead car to ground. My understanding is that the current is flowing from the good battery to the bad battery originating from the negative terminal on the good battery. But this obviously can’t be the case, because then all that current would be flowing right into ground.

Ignore the “ground” for a moment.
If you have two batteries, one good and one dead, you can boost the dead battery by attaching positive to positive and negative to negative. The good battery spills some of it’s charge into the dead one. OK?
Now, replace the negative terminals with the frame of the two cars, and you get the same circuit. We call the frame “ground” but it really is “common” or “return”.

The negative cable is connected to the engine and metal body of the car via grounding straps. It saves wire by using the car as one of the cables. A perfect example is the starter which draws a lot of current. It only has one cable going to it for power.

What does “ground” mean?

Each car is a two-wire system as far as battery power is concerned.

By the way, there is nothing fundamental that says negative must be the grounded side. Some old British cars used to be “positive earth” as we called it.

The electron flow will be out the negitive terminal of the charged battery to the negitive the discharged charged battery and at the same time same time from the positive terminal of the discharged battery to the positive terminal of the charged battery. This is a completed circuit.

The electrons do not flow only one way, ie from a battery to the ground (car body). There has to be a complete circuit.

Ground is a common buss used to replace one of the wires to the battery. The chassis and engine block become part of the circuit, which can be tapped into for an electrical device. That saves having to run a separate negative wire to each device. In the case of the starter, there is only a positive cable running to it. The engine acts as the negative cable and the circuit is completed when the starter is bolted to the engine. Lights and other electrical devices use the chassis to complete the circuit.

But that caused the car to pull to the left.

No it didn’t, it caused them to leak oil.

Think for a second all the electrical items in a modern car. If all of those had to be connected back to the battery via wire, it would easily double the amount of wire in the car, and the negative cable would be the size of an anaconda. Instead the car maker attaches one side of the battery to the frame and engine of the car. (Negative in a modern car, positive in Old British and other old cars) Then to complete a circuit, the car maker supplies power to something and connects the other side to the frame or engine. Ta-Da a complete circuit.