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2020 Mercedes-Benz E-Class — battery dies after the car sits for a weekend

FlatSixDad488Community StarterMar 31, 20262020 Mercedes-Benz E-Class E450Las Vegas
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 in Las Vegas.
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8 replies

WeekendNerd820Community StarterCommunity StarterMar 31, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2020 Mercedes-Benz E-Class so service can see what you saw. That's where I'd start. Not gospel, but it saved me a headache. I'd rather be boring and correct. If the story changes I'll post the new data.
WeekendNerd820Community StarterCommunity StarterMar 31, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2020 Mercedes-Benz E-Class, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. That's where I'd start. On “benz e-class — battery dies after the,” that was the fork that mattered for me. This is from a 2020 Mercedes-Benz E-Class in Las Vegas. Take it or leave it — that's what I'd do. If your situation is the opposite, ignore me. Only after sitting overnight so far.
SunBeltPilot913Community StarterCommunity StarterApr 1, 2026permalink
Agree — and I'd add this: Leave the alerts on the 2020 Mercedes-Benz E-Class so service can see what you saw. I'd do that before spending real money. A shop burned me once by skipping that step. Parking it somewhere I can hear it better next time.
FlatSixDad488Community StarterCommunity StarterApr 1, 2026permalink
OP update: scanned the 2020 Mercedes-Benz E-Class again and still only have the one pending code, no new lights. I'm in no rush to be a hero on it.
FlatSixDad488Community StarterCommunity StarterApr 2, 2026permalink
I went back under the 2020 Mercedes-Benz E-Class and it only happens after a heat soak, not on a cold start. That's my plan before I call anyone.
BrakeCollector333Community StarterCommunity StarterApr 1, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2020 Mercedes-Benz E-Class so service can see what you saw. I'd do that before spending real money. Post the numbers (or the code) and people can get more specific. I'm in no rush to be a hero on it.
SunBeltPilot913Community StarterCommunity StarterApr 1, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2020 Mercedes-Benz E-Class, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. That's where I'd start. On “benz e-class — battery dies after the,” that was the fork that mattered for me. This is from a 2020 Mercedes-Benz E-Class in Las Vegas. Learned this the expensive way on a previous car. Climate here is different, so treat that as a local data point. I'm keeping receipts and dates in one folder.
UsedCarGarage59Community StarterCommunity StarterApr 1, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2020 Mercedes-Benz E-Class — site sharing and pack temp change the curve a lot. Then you'll know the next fork. That's the whole play. I already checked the easy fluid levels.
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