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Audi A6 C6: Why is My Battery Not Charging?

Is your battery suddenly refusing to hold a charge? This article will walk you through the diagnostic process and help you locate, and fix, the source of the problem.

By Brett Foote - April 11, 2016

This article applies to the Audi A6 C6 (2004-2010).

While car batteries oftentimes simply die and leave you stranded out in the cold (or the heat), they can also simply lose their ability to hold a charge. This is especially aggravating because the problem could be the battery itself, or it could be something different altogether. Sometimes the battery might hold a charge for a short period of time, and in other cases it might hold one for a week or more. Whichever situation applies to you, keep reading and we'll walk you through the process of diagnosing the problem and how to fix it.

Audi A6 C6: Why is My Battery Not Charging?

Materials Needed

  • VAG-COM (preferred) or OBD-II scanner
  • Multimeter
  • Screwdriver

Step 1 – Check your relays

Bad relays are easy to check and can cause starting issues.

There are two power supply relays located just underneath the windshield wipers in the engine bay that can cause starting issues when they start to go bad. To check them, simply remove them and tap on each with a screwdriver, then reinstall and try to start the car again. If it starts, you will want to replace the relays, which cost around $25 each.

AUDI DEAD BATTERY WONT START DRAW ALTERNATOR STARTER
Figure 1. Check your power supply relays by tapping on them.

If your relays are working properly, move on to Step 2.

Step 2 – Check the battery and alternator

Either component could be going bad.

The most common cause of charging issues is either a bad battery or alternator. You can have both tested for free at an auto parts store, or you can check them yourself using an alternator. If you have a VAG-COM cable, you can also use the software to see if you are getting an error code for either, or something else.

To test an alternator, turn your multimeter to 20 volts and start the engine. Verify that the alternator pulley and belt aren't loose or slipping. Place the positive (red) probe of the multimeter on the red terminal coming out of the alternator, then place the negative (black) probe on a piece of metal, such as a bolt or part of the car frame. A good alternator will give a reading of somewhere close to 14 volts. Anything less, and the alternator isn't supplying enough power to keep the battery charged.

Next, use your multimeter to check your battery by placing the positive probe on the positive post of the battery, and the negative on the negative. A good battery should read at least 12.6 volts while off, and 13.7 to 14.7 volts while the engine is running. Leave the car off and wait 12 to 24 hours, then check the voltage again. If it drops in that time frame, you will likely need to replace your battery.

AUDI DEAD BATTERY WONT START DRAW ALTERNATOR STARTER
Figure 2. Check your battery and alternator.

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