* Alternator: This is the most common cause. The alternator is responsible for recharging the battery while the engine is running. If it's faulty, it won't recharge the battery, leaving you stranded after turning the engine off. This needs to be tested by a mechanic or auto parts store. They can check the alternator's output voltage while the engine is running.
* Battery: While less likely given the scenario, a very weak battery *could* be part of the problem. A weak battery might accept a charge from the jump start enough to crank the engine, but then it can't hold the charge long enough. Have the battery tested for its ability to hold a charge (CCA – Cold Cranking Amps).
* Wiring: A problem in the wiring between the alternator and battery, or a ground issue, could prevent the charging system from working correctly. A corroded connection is a common culprit. Inspect the battery terminals and cables for corrosion and looseness.
* Voltage Regulator (part of the alternator): The voltage regulator controls the alternator's output. A faulty regulator can lead to overcharging or undercharging, damaging the battery or preventing it from charging properly. This is usually part of the alternator assembly on newer vehicles.
What you should do:
1. Have the battery tested: Take your battery to an auto parts store (like AutoZone, Advance Auto Parts, etc.). They will test it for free and tell you if it's holding a charge properly.
2. Have the alternator tested: This is the most crucial step. The auto parts store can usually test this as well, or you can have a mechanic do it. This test will determine if the alternator is producing the correct voltage.
3. Inspect wiring and connections: Visually check the battery terminals and cables for corrosion or loose connections. Clean and tighten them if necessary.
Don't just replace the battery yet! Replacing the battery without addressing the underlying charging issue is a waste of money; you'll just end up in the same situation. Focus on diagnosing the alternator and wiring first.
