Either the battery or the alternator.

[Sarah_Jane1980]

Seeking further assistance. Attempted to start a 2007 320i convertible with a completely drained battery, even with jump leads. Managed to start the car with booster cables and ran it for about half an hour. Upon returning, noticed a red battery warning light on the dashboard. Unsure if the issue lies with the battery or the alternator.

[jane_doe2023]

What is the voltage shown on the battery? An alternator is not designed to recharge a completely depleted battery. Charge it overnight. How old is the battery?

[Sarah_Jane1980]

Thank you, jane_doe2023. Uncertain of the age but seems ancient. Charged the battery for around 24 hours, attached it to the vehicle, which would not start. Used jumper cables to start the car, left it running for about half an hour in the driveway. When checked, the engine had stopped running and the battery was depleted.

[jane_doe2023]

Increased battery life. I had a battery that failed within.

[Sarah_Jane1980]

Thank you, . Do you believe the issue is with the battery rather than the alternator?

[Samantha_Jones83]

The alternator may also be defective, but you cannot confirm this until the battery is replaced and voltage tests are conducted.

[jane_doe2023]

Alternator or battery? In my opinion, based on what you have said, the issue is likely with the battery as the vehicle should have started after being on a charger for 24 hours. Did the malfunctioning alternator lead to the battery's deterioration? Require the voltage readings to form any understanding. Inform us of your progress.

[Megan_Wilson88]

Install a battery capable of starting the vehicle without jump leads. Monitor for the reappearance of the battery light. If it returns, there may be an issue with the charging system. Obtain a multimeter, even an inexpensive one, to assess the battery voltage and charging voltage.

[Sarah_Jane1980]

Thank you for your responses. They were extremely useful. I am now awaiting the delivery of a new battery. I noticed a significant amount of water behind the battery when I removed it. I am unable to locate a drain or any other mechanism. Any advise on this matter would be appreciated.

[Lucy_Wilson2002]

Ordered a battery from Tayna on Sunday and received it yesterday around supper time with regular delivery.