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Discussion Starter · #1 ·
I am having issues with the 12V battery in my 2020 Ioniq EV with 5000 miles and trying to understand it I am doing something wrong or I have a bad battery. For the last two days, the car is not starting with a message to check regen brakes. I am able to jump start it, but the battery is not holding the charge. When the battery is hooked to the jumper or the car is running I see voltage around 14.3 V, but without it the voltage is 10.1 V.

So my question is, When does the 12V battery charges? Is it only when the car is running, or also when the car is plugged in for main battery charging? Not sure if my 12v battery is not charging or if I have a bad battery.

Thanks,
Sam
 

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So my question is, When does the 12V battery charges? Is it only when the car is running, or also when the car is plugged in for main battery charging? Not sure if my 12v battery is not charging or if I have a bad battery.
Whenever the car is On and ready (i.e. the little green car symbol with the arrows under it is lit, achieved by pressing the power button with your foot on the brake) the DC-DC converter should be powering the 12V systems and simultaneously recharging the battery. Depending on what it thinks the 12V battery state is, you'll see either 14.4V (active charging), 13.8V (float charge), or 12.something (maintain) on the 12V bus. I think they should have just made it 13.8V all the time like a classic fossil car alternator puts out and we'd have a lot less problems. If you're seeing 10.1 with the car on, the DC-DC converter may have a fault. Try getting the battery back to health by disconnecting it and charging with a classic plug-in battery charger, then reconnect it and monitor the voltage while the car is on and ready. If it starts as 12.something but continues to fall, your car's DC-DC converter is definitely out of whack. Good luck!
 
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In addition to charging the 12V battery when the car is on, if you've got Auxiliary Battery Saver+ mode enabled, the main battery will automatically be used to charge the 12V battery when the car is off, as described in this video:

 

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On two separate hyundai vehicles iv had a mare concerning the 12v battery.
In my experience whenever iv had the check brakes warning appear when there's a flat 12volt battery it will very soon leave you high and dry without you being able to even jump start.
I'd be very surprised if the 12v doesn't require replacing.
The problem will be that your dealership will require you booking the vehicle in with them putting it through there bench test but more often than not the result will show the battery is good. But, you'll drive off and at some point become stuck. Its a frustrating situation.
Iv actually paid for a new one and fitted it only when the old one works no longer.
Then taken it into my dealers where its then tested bad and they've then refunded for the new battery.
Good luck.
 

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Apparently this is on ongoing issue with various theories as to what is going on. Visit the poll HERE. Even with the Battery Saver function, it didn't seem to help me. My Ioniq had the 12v battery die at barely 1000 miles on it. The dealer seemed to think it was a defective battery but a lot of people seem to have different opinions on things that might be causing the battery to drain.
 

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Very few batteries have been changed by hyundai given the number of people on here...
They look to be AGM hence the price in some places but hyundai rack up that price too. Eurocarparts in the UK want £40 or £80 for a normal battery for my17 PHEV.

The 12V battery charges when:- (as above)
1 - the car is ON and READY, whether you are driving or not.
2 - when the car is Charging (not just plugged in)
3 - when the battery saver+ kicks in (limited to 5x during an OFF period. (this setting was set to OFF by default but in recent cars it is ON and you can't change it.

Things to avoid (known as operator error) as the battery has 45Ah = half the power of a normal ice 12V battery:-
1 - do not leave the door or boot open when washing or packing the car with the car OFF - switch the car ON
2 - try not to charge at full rate on the grannie charge cable, try a Low or Medium charge setting... This means a charge takes longer but your 12V will be charged for longer too.
3 - as above.... type 2 charger... Alter the car charging setting so that you charge at a lower rate again.
4 - avoid sitting in the car with the radio & lights on with the car OFF. (This happens in older ice cars too - but they need to run the ice. )
5 - make sure you close all the doors and boot fully
6 - make you don't leave the car ON as you walk away despite the buzzer/gongs going off.

Odd things that have caused a battery to drain
1 - water in the door button electronics
2 - poor signal for the blulink app
3 - it is not your key being too close to the car

What can you do:-
1 - monitor the battery via the battery terminals
2 - charge as slower rate to extend the time the 12V is charged via the dc:dc converter.
3 - learn how to open the car with the metal key.. Popping the door handle corner without breaking it... and have a 12V booster ready(or charge the 12V battery)
4 - put the battery on a smart charger each month(or week) in periods of low usage.
5 - MAYBE NOT FOR EVERYONE (mine is a 2017 PHEV and the battery has been low but has never been swapped by the dealer. - I linked a small £20 solar panel 30W 8cm x 25cm permanently to the battery and it sits on the parcel shelf restrained by the cable. There is a connector just outside the battery panel to allow disconnection. (plugging into the cigar lighter will not work).
 

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The 12V battery charges when:- (as above)
3 - when the battery saver+ kicks in (limited to 5x during an OFF period. (this setting was set to OFF by default but in recent cars it is ON and you can't change it.
My car's a late 2020 build. Aux Battery Saver+ was on by default but I can disable it. Has there been a revision since then?

For the people whose 12V batteries have failed - was BlueLink reporting the battery as healthy when it failed?
 

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Discussion Starter · #10 ·
OP here, I have a appointment with the dealer tomorrow. But yes, something is definitely wrong with the battery, I left the car running for an hour and the battery showed 14.3 v (as expected), when I turned the car off, I measured the voltage again and it showed 12.4 V. It started only once again and it did but I could not start it second time. Checked the battery again and it was at ~10.x V. Couple more tries and the battery was reading ~7.7V. Other than the battery gone bad, I am totally dumbfounded as to what is causing such a sharp discharge
 

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12.4V is good but would expect that to drop a slower than that. 11.5V is the worst I've had in 4 years. something is draining yours... Or it needs to be swapped.
Is Blue link up to no good?
 

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I fitted an SAE charge lead to my 12 volt battery and put it on charge every 2 months.
If I have a long trip away from home - I also top up again the day before.
Using an Optimate smart charger.

There are so many reports about 12 volt batteries failing in EV's (not just Hyundai).
It looks to me that whatever the manufactures designed to maintain the 12v, it is just not working reliably.
 

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OP here, I have a appointment with the dealer tomorrow. But yes, something is definitely wrong with the battery, I left the car running for an hour and the battery showed 14.3 v (as expected), when I turned the car off, I measured the voltage again and it showed 12.4 V. It started only once again and it did but I could not start it second time. Checked the battery again and it was at ~10.x V. Couple more tries and the battery was reading ~7.7V. Other than the battery gone bad, I am totally dumbfounded as to what is causing such a sharp discharge
Not discharging from vampire current, that is how damaged batteries behave even without a load.
 

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Had 12 V trouble with my PHEV this winter, mostly short trips, short charging periods. After two days parked in -12 C it was dead. At service, a week ago, I had both battery checked (again) and the charging voltage - both perfect.

I have my share of battery problems over the years (~45), but never with car and battery less than 5 years old. I won't dare parking my PHEV away from home, for more than a day - in cold winter - without a portable, cordless charger.

I wonder why it will only charge the 12V from the main 5 times.
 

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I wonder why it will only charge the 12V from the main 5 times.
So the traction battery doesn't get too low and become damaged. You may have never seen this dialog in a PHEV, but when you get low on fuel there is a warning to fill up now so you don't damage your battery. Same rationale, only that unlimited charges will indeed damage your traction battery.

In an HEV, I've seen this warning many times, almost every time I before (like 100 miles before) I fill up the tank.
 

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So the traction battery doesn't get too low and become damaged. before (like 100 miles before) I fill up the tank.
The traction battery may be fully charged - still. Can't see why limit by number is the only way to protect it.
 
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