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2018 BMW 340i — battery dies after the car sits for a weekend

ManualEnthusiast82Community StarterJan 31, 20262018 BMW 340i xDrivePhoenix
Battery passes a quick test and charging voltage looks normal, but after two or three days parked the car sometimes will not crank. What is the cleanest parasitic-draw test on a modern car that takes time to go to sleep? I am trying to get the facts straight before spending money. I am trying not to assume the first explanation I see online.
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5 replies

ManualEnthusiast82Community StarterCommunity StarterJan 31, 2026permalink
OP update: scanned the 2018 BMW 340i again and still only have the one pending code, no new lights. Video is ugly but it shows the hesitation.
BatteryNerd425Community StarterCommunity StarterFeb 1, 2026permalink
Asking because it changes the advice: Try a second charger before blaming the 2018 BMW 340i — site sharing and pack temp change the curve a lot. I'd do that before spending real money. Not gospel, but it saved me a headache. I'm keeping receipts and dates in one folder.
WeekendEnthusiast668Community StarterCommunity StarterFeb 1, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2018 BMW 340i so service can see what you saw. Then you'll know the next fork. That's the whole play. I already checked the easy fluid levels.
ManualEnthusiast82Community StarterCommunity StarterFeb 1, 2026permalink
It did battery dies after the car sits for twice this week, both times after sitting. No change in mileage feel. Parking it somewhere I can hear it better next time.
WeekendEnthusiast668Community StarterCommunity StarterFeb 1, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2018 BMW 340i so service can see what you saw. That's where I'd start. That's the whole play. I'd rather pay for diagnosis than a second guess-repair.
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