My 12 Volt battery is dying..

[FloridaSun]

Woke up to a dead 12 Volt battery for the 2nd time in 3 weeks. I do have a small Li-Ion EV jump start battery, so I was able to start the car.. I'm not sure if it's the battery itself as when it went dead 3 weeks ago, I was able to get it to 87% SoC and when I checked a few times in the morning after that, it was still 86 to 87%.. Today, I jumped it again and drove for 1.5 hours.. SoC of the 12V battery is now at under 30%. I believe that something is draining it on some nights.. Will have to bring the car to Hyundai on Monday to check what's going on..
After some discussion on a facebook Kona group, it appears that it may have something to do with my OBD2 dongle which I often leave plugged in all night long...
My 12 Volt seems to be past it's useful life as it shows 27% SoC right now after driving 150 miles today...

 

[Tomek]

I saw a post there, pointing that the trunk lid may be not fully closed causing the charging of the 12V batt by the HV batt is impossible for an unknown reason.

 

[FloridaSun]

I saw a post there, pointing that the trunk lid may be not fully closed causing the charging of the 12V batt by the HV batt is impossible for an unknown reason.

Trunk was closed but OBD2 dongle was plugged in..

This morning, the car was not dead.. I checked the battery and the SoC of the 12 Volt went from 27% when I parked it last night to 85% this morning.. Weird.. I did make sure that the OBD2 dongle was not plugged in overnight..

 

[KiwiME]

Personally I'd put no faith in that aux SoC reading without fully testing it. Even then we know the car has difficulty understanding the aux battery's condition.
As I mentioned before on FB, best to instead measure the settled open-circuit voltage without disturbing the car. Unless you run wires from the aux battery to the outside so you can check this with a voltmeter without opening the hood, the only practical way to do that is with a BM2.

 

[FloridaSun]

checked the 12 Volt again this morning.. It's at 85%, so it must've been the OBD2 dongle that ran down the battery.. I have to remember to unplug it every time I use it..

 

[Joev]

Personally I'd put no faith in that aux SoC reading without fully testing it. Even then we know the car has difficulty understanding the aux battery's condition.
As I mentioned before on FB, best to instead measure the settled open-circuit voltage without disturbing the car. Unless you run wires from the aux battery to the outside so you can check this with a voltmeter without opening the hood, the only practical way to do that is with a BM2.

I disconnected the hood switch so I can monitor things without the dashboard indicater coming on. Follow the wiring to the left from the hood latch release switch, there is a simple plug, unplug that (and tape it up so no dirt or moisture gets in it), have had it like that for a year, no issues.

 

[electriceddy]

I disconnected the hood switch so I can monitor things without the dashboard indicater coming on. Follow the wiring to the left from the hood latch release switch, there is a simple plug, unplug that (and tape it up so no dirt or moisture gets in it), have had it like that for a year, no issues.

Here is a picture of it below the hood support rod seat:

I found that the alarm system activated if you tried to leave it unplugged and closed the hood when the car is shut down and locked.
There is probably an identical switch for the tailgate which I am going to investigate this summer. By disconnecting that one it may resolve the 12 V battery dying when leaving the tailgate ajar, and may allow driving with the tailgate tied down but not latched to enable carry long loads without the obnoxious warning on the dash.

 

[Esprit1st]

Finally I'm joining you guys. After pretty much exactly 2 years (and 3 days) my 12V was dead this morning. Strangely enough after just having done a ~400 mile road trip yesterday and the day before.

I have a small 12V battery pack, but right now the car stays in "run mode" in the parking lot, so I'm good to go while running a few errands.

 

[FloridaSun]

I had my car at Hyundai and they couldn't find anything wrong with it.. Problem is that I had driven already for a day after the battery went dead and it showed over 80% SoC again... I guess I have to wait until it happens again and bring the car in right after the battery was dead..