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2018 A4 Battery Draining Fast - "Battery Low" Warning

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Chris P. · rep 0 · May 22, 4:28 AM · 1 replies · solved · Question

Vehicle: 2018 Audi A4 Premium Plus

I've got a 2018 Audi A4 Premium Plus, and lately, I've been getting a "Battery Low" warning on the dash, especially after the car sits for a day or two without being driven. Sometimes it even struggles to start, almost like the battery is dead.

I had the battery tested at a local auto parts store, and they said it was okay, holding a good charge, but it still feels like something is draining it overnight or when parked for extended periods. I don't have any aftermarket accessories installed.

Could it be a faulty sensor, a module not shutting down, or something else electrical causing a parasitic draw? I'm worried about getting stranded.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:28 AM

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ClearTheCode admin answer: A "Battery Low" warning and quick battery drain in your 2018 Audi A4 Premium Plus, especially after the battery tests "good," strongly suggests a parasitic draw or an issue with the charging system.

  1. Check for Parasitic Draw: This is when an electrical component continues to draw power even when the car is off. Common culprits include:
    • Faulty Modules: A control module (e.g., infotainment, comfort control, gateway) that isn't properly "sleeping" or shutting down.
    • Stuck Relays: A relay that remains energized.
    • Trunk/Glove Box Lights: Lights that stay on due to a faulty switch.
  2. Inspect the Charging System: Even if the battery is good, a failing alternator or voltage regulator won't properly recharge it.
    • Alternator Output: A shop can test the alternator's output voltage and current under load. It should typically be between 13.5V and 14.5V.
    • Belt Tension: Ensure the serpentine belt driving the alternator is in good condition and properly tensioned.
  3. Battery Management System (BMS): Audi vehicles use a sophisticated BMS. A fault within this system or its sensor (often on the negative battery terminal) can lead to incorrect charging or battery monitoring, even if the battery itself is healthy.
  4. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for codes related to the charging system or electrical faults. Relevant codes might include:
    • P0562: System Voltage Low
    • P0620: Generator Control Circuit Malfunction
    • P065B: Generator Control Circuit Range/Performance
    • U-codes: Communication errors between modules, which could indicate a module not shutting down.

When to See a Shop: If you've confirmed the battery is healthy and the problem persists, it's crucial to visit an Audi dealership or a qualified independent European car specialist. Diagnosing a parasitic draw can be complex and time-consuming, requiring specialized tools and knowledge to systematically isolate the faulty circuit or module. Ignoring a persistent battery drain can lead to repeated no-starts, potential damage to the battery, and even issues with other electrical components due to low voltage.

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