* Alternator Failure: This is the most common cause. The alternator is responsible for charging the battery while the engine is running. If it fails, the battery drains, and the car will eventually stall. A failing alternator might initially produce erratic voltage, causing the jerking you describe.
* Battery Failure: While less likely to cause the jerking, a completely dead or severely weak battery can cause the car to stall. The battery light will illuminate because the alternator isn't able to charge a completely depleted battery.
* Bad Battery Cables or Connections: Corroded, loose, or damaged battery cables can prevent sufficient power from reaching the alternator or the battery itself, leading to similar symptoms.
* Voltage Regulator Failure (part of the alternator): The voltage regulator controls the output of the alternator. If it fails, the alternator might overcharge or undercharge the battery, causing the light to come on and potentially leading to stalling.
* Faulty Wiring: A short circuit or other wiring problem somewhere in the charging system can also interrupt the flow of electricity, leading to the symptoms you describe.
* Ignition System Issues (less likely): While less directly related to the battery light, severe problems with the ignition system *could* coincidentally cause a stall and trigger the battery light as a secondary effect of a voltage drop. This is less likely given the jerking description.
What to do:
1. Check the battery terminals: Look for corrosion. Clean them if necessary with a wire brush and baking soda solution. Tighten the connections.
2. Have the alternator and battery tested: A mechanic can test both components to see if they are functioning correctly. This is the most important step. Don't just replace parts based on speculation.
3. Inspect the wiring: While this is harder to do yourself, a mechanic can visually inspect the wiring harness for any obvious damage or loose connections.
Important Note: Driving with a malfunctioning charging system is risky. You could become stranded if the battery completely dies. Get it checked out by a mechanic as soon as possible.
