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Every few months we have an issue where the battery in my 2006 Audi Avant dies. I've taken it to a battery place and they say that it's perfectly healthy. So I bought a BLE battery monitor and now I'm watching the battery do it's thing. I do know that the battery might not be getting fully charged after each drive since I usually only drive for about 5-10 minutes at a time. After several weeks it finally did the big drop again and I have data recording what happened.

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You can see that the last time we drove the car was May 19 and then didn't drive it at all on May 20, then sometime during May 21 the battery level collapsed.

What might cause something like this?

What else besides this battery monitor might I use to diagnose this problem?

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  • Welcome to Motor Vehicle Maintenance & Repair! Is this an AGM battery? Could you put up the model number of whatever type it is? May 22, 2023 at 22:43

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There is a vertical line down to just under 12v in the early hours of the 21st indicating that something has turned on. The voltage then drops steadily until midday where it drops below 9v, so current is still being drawn. At some point it then turns off and the battery voltage starts to creep back up. Early next morning, it switches back on and the voltage quickly drops again.

You need to find out what is switching on. You could set a camera up to watch for lights coming on. This could be automatic headlights, or the ECU may be turning on so the dash light could be illuminating. I guess you could just go and have a look when you get up on the morning, because the current is still on until fairly late in the morning.

If that doesn’t reveal anything, you may need to start pulling fuses to identify which circuit is drawing current.

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  • It also looks as though the power draw starts occurring right around the same time each day on the 20th & 21st. This seems to me to be odd behavior, because you don't see it happening on any of the other 13 days shown in the graph. It seems like it is a pretty hefty draw, too. If we had a more granular graph of the 20/21st as well as a reserve capacity of the battery, we could probably figure out how much draw is occurring during that time. May 23, 2023 at 9:55

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