There are lots of threads about dead 12V batteries and EVs, but they almost all talk about theories, or they are for the IONIQ 28kWh pre-2020 models. So, I figured I'd post my slightly different experience - and YES, my problem is still ongoing.
I bought my 2020 IONIQ 38kWh new in Oct 2020. It ran nicely until May 2021 when I experienced the dead 12V battery problem. I took it back to the dealer and they said that the 12V battery sensor had "blown" and so the Big battery was not able to detect and to charge the Small battery. They changed the sensor under the warranty. NOTE this model EV, unlike the earlier models (which I also had owned) does not have a Battery+ Saver setting - it always charges the 12V battery when it needs it.
The car then ran nicely until Nov 2021 when once again it suffered a total failure of the 12V battery. This time the dealer declared that the battery was faulty and changed it under the warranty. For info: the battery is a 12V 40AH AGM battery.
The car then ran nicely until Oct 2023 when we left it in an airport car park for 1 week. Again the 12V battery was dead. We called out a breakdown service and they jump started the car and recommended that we get the battery checked as their device was indicating a bad battery. We took it back to the dealer who said that the battery was OK, and that the problem was once again the battery sensor which, this time, was draining the power off the 12V battery. They changed the battery sensor again under the warranty. Meanwhile, we bought a 12V lithium jump start device and kept it in the glove box.
The car then ran nicely until Apr 2024 when, after leaving it at home for a week whilst we went away in our other car, and after a few fairly short runs when we got home, the 12V battery died once again. It is being returned to the dealer again next week for them to diagnose and fix. Meanwhile I bought a clamp meter and a better smart charger - the previous model, although excellent, charged at 5A max and that wasn't sufficient to get the battery up and running again whilst whatever was draining it was still active - the new charger has 10A charge capability plus battery recovery and repair features.
Here is what I observed after this last failure:-
I bought my 2020 IONIQ 38kWh new in Oct 2020. It ran nicely until May 2021 when I experienced the dead 12V battery problem. I took it back to the dealer and they said that the 12V battery sensor had "blown" and so the Big battery was not able to detect and to charge the Small battery. They changed the sensor under the warranty. NOTE this model EV, unlike the earlier models (which I also had owned) does not have a Battery+ Saver setting - it always charges the 12V battery when it needs it.
The car then ran nicely until Nov 2021 when once again it suffered a total failure of the 12V battery. This time the dealer declared that the battery was faulty and changed it under the warranty. For info: the battery is a 12V 40AH AGM battery.
The car then ran nicely until Oct 2023 when we left it in an airport car park for 1 week. Again the 12V battery was dead. We called out a breakdown service and they jump started the car and recommended that we get the battery checked as their device was indicating a bad battery. We took it back to the dealer who said that the battery was OK, and that the problem was once again the battery sensor which, this time, was draining the power off the 12V battery. They changed the battery sensor again under the warranty. Meanwhile, we bought a 12V lithium jump start device and kept it in the glove box.
The car then ran nicely until Apr 2024 when, after leaving it at home for a week whilst we went away in our other car, and after a few fairly short runs when we got home, the 12V battery died once again. It is being returned to the dealer again next week for them to diagnose and fix. Meanwhile I bought a clamp meter and a better smart charger - the previous model, although excellent, charged at 5A max and that wasn't sufficient to get the battery up and running again whilst whatever was draining it was still active - the new charger has 10A charge capability plus battery recovery and repair features.
Here is what I observed after this last failure:-
- Wed 17th Apr 2024. Battery dead at 6.2V. Turned off: seat easy access, wireless charging, Bluelink set to offline mode. Recharged the battery with the new smart charger. After being fully charged, the drain registered 0.4A.
- Sat 20th Apr. Battery dead - haven't driven the car - just tried unlocking the doors. With the car unlocked but not started, doors closed but bonnet open, it showed a drain of 4.1 amps. I decided that was not correct so: I reset the meter and turned the lights on (side lights since car not switched on) and saw a 3.5A discharge; turned the lights off, closed the doors, waited for the interior lights to go out - no appreciable discharge - 0.2A. But the battery was reading 7.2V. Recharged the battery to full.
- Today Tue 23 Apr. Battery dead - still haven't driven the car - just tried unlocking the doors.
