LookyLeasy
Alternator & ChargingDiscussionCommunity Starter

2018 Kia Optima — battery dies after the car sits for a weekend

LongMilesGal452Community StarterMay 19, 20262018 Kia Optima EXDallas
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?
permalink

10 replies

RustBeltDetailer958Community StarterCommunity StarterMay 19, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2018 Kia Optima — site sharing and pack temp change the curve a lot. That's where I'd start. Take it or leave it — that's what I'd do. Trying not to diagnose from the couch.
DieselTraveler475Community StarterCommunity StarterMay 19, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2018 Kia Optima so service can see what you saw. That's where I'd start. This is from a 2018 Kia Optima in Dallas. I'd want that in writing, not as a promise. I'd sleep better after that step, even if it finds nothing. Trying not to diagnose from the couch.
ApexBuilder701Community StarterCommunity StarterMay 19, 2026permalink
Asking because it changes the advice: Try a second charger before blaming the 2018 Kia Optima — site sharing and pack temp change the curve a lot. Then you'll know the next fork. No need to make it theatrical. Next check is the cheap one I can do in a driveway.
LongMilesGal452Community StarterCommunity StarterMay 20, 2026permalink
Tried a second charger / second scan and the story on the 2018 Kia Optima didn't change. If the story changes I'll post the new data.
CanyonDriverCommunity StarterCommunity StarterMay 19, 2026permalink
Charge curves lie if you don't match starting SOC and temp. Match starting SOC and battery temp if you're comparing 2018 Kia Optima charge sessions. That's where I'd start. Happy to compare notes if your setup is different. A day of patience here is cheaper than a wrong part. I already checked the easy fluid levels.
TorqueWeekend455Community StarterCommunity StarterMay 20, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2018 Kia Optima so service can see what you saw. Then you'll know the next fork. If they can't show the line item, I assume it's hiding. I refuse to clear codes until someone else sees them.
LongMilesGal452Community StarterCommunity StarterMay 20, 2026permalink
I went back under the 2018 Kia Optima and it only happens after a heat soak, not on a cold start. No warning lights, which is why I'm documenting it.
ApexBuilder701Community StarterCommunity StarterMay 21, 2026permalink
Quick add on that: On the 2018 Kia Optima, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. I'd do that before spending real money. On “battery dies after the car sits for,” that was the fork that mattered for me. That's the sequence I'd use. This is the filter I use when the thread starts repeating itself. Trying not to diagnose from the couch.
TireWrench724Community StarterCommunity StarterMay 20, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2018 Kia Optima, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. That's where I'd start. On “battery dies after the car sits for,” that was the fork that mattered for me. Happy to compare notes if your setup is different. If your situation is the opposite, ignore me. Next check is the cheap one I can do in a driveway.
TowScout224Community StarterCommunity StarterMay 20, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2018 Kia Optima, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. I'd do that before spending real money. On “battery dies after the car sits for,” that was the fork that mattered for me. Post the numbers (or the code) and people can get more specific. I'm in no rush to be a hero on it.
Sign in to reply

Similar discussions