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2018 Cadillac CTS-V — battery dies after the car sits for a weekend

CanyonGarageCommunity StarterAug 16, 20262018 Cadillac CTS-VSeattle
2018 Cadillac CTS-V, about 92,000 miles. 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?
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7 replies

RoadTripDadCommunity StarterCommunity StarterAug 16, 2026permalink
Intermittent stuff lies if you only catch it once. Write temp, speed, and in-gear vs coast when the 2018 Cadillac CTS-V does it — then decide on parts. Don't erase codes until someone who can help has seen them. On “v — battery dies after the car,” that was the fork that mattered for me. If it doesn't change the out-the-door or the repair estimate, it's noise. This is the filter I use when the thread starts repeating itself. This is the version I'd tell a friend.
CanyonGarageCommunity StarterCommunity StarterAug 16, 2026permalink
Tried a second charger / second scan and the story on the 2018 Cadillac CTS-V didn't change. No warning lights, which is why I'm documenting it.
FlatSixSeller714Community StarterCommunity StarterAug 16, 2026permalink
I'd want a measurement, not a hunch. Write temp, speed, and in-gear vs coast when the 2018 Cadillac CTS-V does it — then decide on parts. Don't erase codes until someone who can help has seen them. This is from a 2018 Cadillac CTS-V in Seattle with 92,000 miles. Did the worksheet show tax yet? I'd rather be boring and correct. Heat soak after errands is the other window.
RoadTripDadCommunity StarterCommunity StarterAug 17, 2026permalink
This is usually cheaper to test than to guess. Move a coil or plug on the 2018 Cadillac CTS-V if it's cylinder-specific and see whether the code follows. If the cheap test changes it, stop and reassess. I'd want a dollar figure or a measured spec, not 'should be fine.' Not interested in a five-hour wait for a shrug.
DieselScout63Community StarterCommunity StarterAug 17, 2026permalink
Log the conditions before you spend. Write temp, speed, and in-gear vs coast when the 2018 Cadillac CTS-V does it — then decide on parts. If the cheap test changes it, stop and reassess. On “v — battery dies after the car,” that was the fork that mattered for me. Run the total, not the monthly, before you commit. Climate here is different, so treat that as a local data point. This is the version I'd tell a friend.
BatteryScout447Community StarterCommunity StarterAug 18, 2026permalink
That's a good start, but I wouldn't stop there. Two 2018 Cadillac CTS-Vs can feel identical and have different causes, so measure before you copy someone else's repair. If the cheap test changes it, stop and reassess. This is from a 2018 Cadillac CTS-V in Seattle with 92,000 miles. That's the whole play. Checking again after work.
RoadTripDadCommunity StarterCommunity StarterAug 17, 2026permalink
If it were in my driveway, loaded-suspension checks on the 2018 Cadillac CTS-V catch play that a wheels-hanging inspection misses. You'll know quickly if you're on the wrong tree. I'd want a dollar figure or a measured spec, not 'should be fine.' Heat soak after errands is the other window.
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