Hi, our 2022 Tucson PHEV has been running fine for the past 11 months, but after sitting idle 2 weeks while we were on vacation, it became totally dead and required the manual key for entry. So I then popped the hood, jump-started from the fuse box, and test drove it just fine. Dashboard shows exactly half tank of gas, and 75% battery; exactly as I had left it 2 weeks ago.

After the test drive, when turning off the car, the dashboard flickers for 10 seconds and all is dead again, which means it needs a jump-start everytime now.

Dealer service center wants me to leave the car w/hem for a couple weeks, and they'll try to look at it.

Does anybody have any ideas or advice? Thanks!

 

I put a trickle-charger on the boosting points under the hood

By "boosting points under the hood", do you mean the positive terminal in the fuse box?

My manual page 9-33 says under "By jump starting" to drive for 20-30 minutes before shutoff. I only test drove 10 minutes, which didn't help, so I'll try the 30 minutes...

 

So after jump-starting it a 2nd time, I drove over 30 mins, and appears to have done the trick. Now I can start the PHEV normally. Probably doesn't matter, but I drove mostly in sport/gas mode, because I'm not 100% sure whether the starter battery would charge from only the main battery running (EV mode).

But had to jump-start again. Maybe because I switched to Eco/EV mode?

So now I'm back to Sport mode, and have successfully shutdown/started a few times over several hours. Still have the Malfunction Light Lamp showing on dash though. For now, am leaving radio off, AC off, and use of MyHyundai app just in case they increase the power required during starting the car or drain the 12v battery.

I see the 12v/start battery under cargo floor. It was 13.76 volts, which sounds healthy to me.

 

Interesting. I have my service appointment tomorrow so I'm hoping to have a few more answers. What ended up working for me was removing the negative terminal and charging with the trickle charger directly on the 12 Volt battery for about 18 hours. Your 13.76 volts may be reading the voltage with the DC-DC charger engaged, and not actually the battery voltage. I'll add more after my appointment...

 

Your 13.76 volts may be reading the voltage with the DC-DC charger engaged, and not actually the battery voltage

Yeah, I didn't try checking voltage until after jump-starting and driving around.

Now it's the second day, and car is reliably starting, and MIL light has gone away on its own.

 

Tkenopic, thanks for starting this thread. Sorry for the long post but anyway here's my experience and thoughts-

I've had my Tucson PHEV for 1 year 14,000 mi without issue, then last week had the same problem of the 12V battery being discharged excessively, and then the car not starting. I had only not used the car for about a week, and initially it started, then I had driven about 15 minutes, stopped at a bank for a few minutes, then when I went to leave it wouldn't start. The console and touchscreen display were on and there was a low battery message on the touchscreen, which I didn't see at first. I called the dealer and they made me have it towed there when now I know I could have jumped it and driven the 30 min etc to recharge the battery as you guys describe. They just charged the battery.

But the dealer tech guy didn't offer any real solution to what seems to be a major design flaw in the handling of the 12V system in these cars. Per the manual, which is for both the hybrid and PHEV, the hybrid apparently has a lithium 12V battery integrated into the main lithium battery. And as you have mentioned, the hybrid has a 12V battery reset switch which allows you to start the car, despite the low battery (presumably as long as it is not too discharged), and then leave it on for a while to recharge the 12V battery. Apparently, the engine doesn't have to be running to charge the battery, since it seems to charge directly from the main lithium battery. Why they went to a separate lead acid 12V battery for the PHEV is not clear, and also not clear why they don't have the battery reset switch or some other software method to keep the battery from getting excessively discharged after short periods of non-use, or a lot of accessory use.

Elsewhere in this forum, someone posted a link to a YouTube video about the Ioniq EV having a "auxiliary battery saver" function in the software that is on by default, but user selectable to turn on or off, and this supposedly helps save the 12V battery from excessive discharge. I scoured the software menus in my car and didn't see anything about this, and also nothing in the manual. I wonder if this is a software update that they could do for the PHEVs.

I will be interested to hear what your dealer has to say, I'm not too thrilled with mine's response. I will be leaving the car at long-term airport parking in a couple weeks, for about 10 days, and I am planning on just disconnecting the negative battery terminal to prevent any drain so I don't need a jumpstart when I get back.

Any other suggestions/info on this will be appreciated.

 

How do you disconnect the negative battery terminal? I have had 6 occurences of trying to start my PHEV with a dead battery. Looking for a long term solution!

 

long-term airport parking in a couple weeks, for about 10 days, and I am planning on just disconnecting the negative battery terminal

Actually , I can't envision that working out: say you pressed door-lock prior to disconnecting the 12v battery under the cargo floor. Then to close the trunk, you'd have to resort to physically pushing it closed and hopefully it'd lock. Then upon your return, you'd need to do the manual key entry, where you could then easily pop the hood, but for the trunk, perhaps you'd have to climb into the cargo area and unlatch it somehow.

Regardless, you'd probably want to pop off the door handle cover for the manual key prior to driving off to the airport, so that you don't risk dropping it and having to crawl around trying to find it.

Would be nice if there was an equivalent way of disconnecting the battery from the fusebox under the hood.

BTW, I have a small portable jump-starter, which, when it was used to jump-start our ICE minivan, used up much of its charge; perhaps it had enough juice to do two such jump starts. But with the PHEV, very little charge is used each time; it still shows all 4 bars of full charge even after 5 jump-starts of the PHEV.

 

Actually , I can't envision that working out: say you pressed door-lock prior to disconnecting the 12v battery under the cargo floor. Then to close the trunk, you'd have to resort to physically pushing it closed and hopefully it'd lock. Then upon your return, you'd need to do the manual key entry, where you could then easily pop the hood, but for the trunk, perhaps you'd have to climb into the cargo area and unlatch it somehow.

Regardless, you'd probably want to pop off the door handle cover for the manual key prior to driving off to the airport, so that you don't risk dropping it and having to crawl around trying to find it.

Would be nice if there was an equivalent way of disconnecting the battery from the fusebox under the hood.

BTW, I have a small portable jump-starter, which, when it was used to jump-start our ICE minivan, used up much of its charge; perhaps it had enough juice to do two such jump starts. But with the PHEV, very little charge is used each time; it still shows all 4 bars of full charge even after 5 jump-starts of the PHEV.

Thanks, you’re right, getting into car would be a hassle without power. The portable jump starter is an idea, but I’d still have to use the manual key entry to get it out of the car if the battery does go dead. But maybe the battery will last the 9 days without unhooking it. So you’ve had to jump your PHEV multiple times? Great.

 

Another idea: If it turns out that the 12v battery gets charged anytime the car is running at all, even when parked, regardless of whether the engine is running, then while the car is sitting idle for an extended period, use the MyHyundai app to perform a remote start every few days, for a few minutes each time... And if for some reason the remote shutoff fails or is forgotten, presumably some timer will kick in and force the shutoff anyway.

 

Bluelink is disabled after about 3 to 4 days unless the car is physically started. (Because it is one more thing that drains the battery.)

 

FWIW. Very good idea to get a voltmeter and install it in the car: see piccie below. Cheap insurance as I've often said. Beyond that, once you've drained your battery, its days are numbered. Depending on how deeply you discharge it, it might be done NOW. Do this 3 or 4 times, and even e new battery is through. Sometimes even though you can recharge them, they won't hold a charge for long. Solution? Get a new battery. Not sure what kind it is? Just look at it carefully. It will tell you. Or just test it: a standard lead/acid will hold 12.2-12 8 volts while resting, but never higher. If it's any lower than that, likely that it's shot. A standard lithium-iron-phosphate battery should hold at least about .5 volts higher at rest, 13.1-13.2 volts is normal.

 

My battery has died 6 tiimes and it shows 82% health. Does that mean it won't hold a charge as long anymore? And that it will never charge to 100%?

Where did you get the voltmeter and how did you install it?

 

OK so not much help from my appointment. It just seems like the techs and supervisors are run off their feet, and don't have time to look into deep details. He has messaged his warranty contact with my questions but no response yet. He did point out a couple options but then ruled them out. For example, there is a 'ship mode' that the cars are put in once they are built but before they are sent to dealers. Unfortunately, this can only be engaged with the dealer technician plugging a tablet into the car electronics. The other thing he mentioned is that previous models (hybrid only) had a switch under the dash that you could engage, but the PHEV doesn't have one. He said, honestly if you can't find an answer on the forum, I'm not likely going to be able to help either. LOL.

There has to be SOMEONE at the head office that specializes in PHEV. If anyone finds a contact, that would be great. Here are the items I think we need answers to:
Hyundai PHEV

1. 12 volt battery specs (amp hours, chemistry, group size, CCA)
2. Which systems use 12 volt and what is their draw in amps
3. Alternator vs dc dc charger
4. Ev mode why does ice comes on
5. Current demand at start up
6. Parasitic draw on stand by (in amps - someone suggested 50 milliamps)
7. Bypass for vacation mode?
8. Resolution? Ioniq software update? Connection to lithium?

 

Hyundai should be using AGM batteries on these hybrid, PHEV and EV's. Our Prius V from 2014 to early 2025 never had this problem, our new 2025 Hyundai Tucson Ultimate PHEV has had it several times and once catastrophically bad. The charger for the traction battery would not run, just blinking red light and the Tucson would not boost from under the hood. I had to remove the back covers etc and boost directly on the battery to get it to start! My CAA insurance module was drawing a fair bit of battery all the time apparently so we ended up removing it and have not had to boost the car since however an AGM battery probably would not have had this problem in the first place!

 

Would never have gotten a Tucson PHEV if I had known that it needs a jump start after sitting for 2 weeks

 

Ya, serious engineering design flaw, disappointing. There HAS to be someone working on this though right? There's so many people reporting the same issue...

 

Hyundai for the Ionic 5 solved this same dead battery issue, what I don't know is if the Tucson PHEV is the same.

The Integrated Charging Control Unit (ICCU) was the issue for the 12v battery being dead.....

 

Right, I heard that also, put in my list of questions, but CSM or tech hadn't heard if that solution...

 

Wondering if one of these simple solutions might work?
-- hook up a battery tender to the 12v battery while on vacation.
--No electricity available? Maybe hook up this same tender to a battery source like this one: CLICKY. Prices have come way down since I bought mine 4 years ago. I do this routinely with my Honda Gold Wing as the starting battery doesn't have enough reserve to survive the parasitic draw of the computer for more than a few days.
If you can count on some significant sunshine, you might try this solar battery charger by Schumaker. They are a reputable manufacturer. CLICKY

 

So I ran a few tests today. With the car locked and 'at rest' parasitic draw was about 0.2 amps. Starting the car without my foot on the brake it went into 'active' mode and was drawing 20amps! So basically all of those start up systems are drawing from the little 12 volt, which is crazy when you have 15kW of power just sitting there. Good news is that the DC-DC charger starts as soon as the car starts. When I put my foot on the brake and started in EV mode, just sitting in the driveway, it began charging the 12 Volt at about 14 amps. I turned it off again, to see what happens when it's plugged in. Turned off the car, plugged it in and locked it. While charging, it ALSO charges the 12 Volt battery which is good (I wasn't sure that it would). I was getting about 12 amps/14.4 Volts. When we go away next, my plan is to leave it plugged in and hopefully when I come back the 12 Volt is still charged. I'll let you know. Photos below for context...

 

Well there ya go. So many struggle with keeping their 12v battery charged up when they're away from the car for awhile. Now we know approximately what the parasitic draw is. You're right. .2 amps is pretty significant for a constant drain on such a small 12v. battery. No wonder bad things happen after a few days of that stuff. Hopefully, between your input and that of the rest of the forum here, we've provided some answers.

 

So in my prior post I mentioned about a "aux battery saver" function (aux battery being the 12V) that apparently the Tucson hybrid and other hybrids have, and initially I didn't see anything about it in the manual for the PHEV. Well there is something about it in the manual, but I wonder if this system is not actually installed or active in the PHEV- can't find it in the system settings when the manual says it's supposed to be there. Sounds like as long as there is enough charge in the Li main battery, or the ICE is running, this is supposed to keep the 12V charged. But if the Li battery is too low, and the car is not running, it probably won't work. Or as mentioned in the text, if the battery saver function activates too many times in a row, it stops trying, assuming there is a problem with the 12V battery. In the 2022 manual it's page 1-42 and 43 and in the 2023 manual it's 1-54 and 55. Screen shots of the section are below:

I'm going to ask the dealer about it- not they will know anything. I'm wondering if maybe it was decided to not have this system user selectable, and it's there just supposed to be always on. And maybe if so it just isn't that effective, and won't be if the car is sitting too long with the Li battery low. For what it's worth...

 

...Sounds like as long as there is enough charge in the Li main battery, or the ICE is running, this is supposed to keep the 12V charged...

Thanks for posting. We might have something here...

 

Did you ever end up testing your theory re: locking the doors and leaving the car plugged in when you travel? If so, what was the result?

 

Yes. Left for a week plugged in and no issues starting or running afterwards. Like my post above, AC charges the lithium and the DC to DC charger on-board charges the 12volt starting battery

 

Sorry to necro-bump this thread but I also have a 2024 Tucson PHEV with similar issues.

Two times now, my wife has come to the car after a 12 hour work shift with the car completely dead.

Our leading theory is that this is caused by the way she plugs the car in at work.
Let me explain:
1) She arrives at work and plugs into a ChargePoint plug
2) The ChargePoint is free for four hours
3) most days she’s able to get a break to move the car before the four hours is up
4) Some days she doesn’t get the chance to move and unplug the car. Those days, once the car is fully charged, she ends the Session in the ChargePoint app so that she doesn’t get charged $$ for charging for more than 4 hours.
5) Twice now since it’s gotten colder, she has ended work and come to a completely dead car.
6) both times were times when she just ended the session in the ChargePoint app but did not unplug the car.

So our theory is as follows:
When the car is plugged in but the ChargePoint session is ended, the car keeps requesting power and keeping the auxiliary systems on. This drains the 12v battery completely.

There are a few holes in this theory though.
Both my home charger (emporia) and the car itself offer charge scheduling capabilities.
Is it really realistic to think that a car that is requesting a charge but not getting it repeatedly would drain the 12v since it would just be us using the scheduling function.

@tkenopic - since you seem to have the most experience with our cars, I would love your perspective on the above situation.

I’m worried taking the car to the dealership would be a futile exercise where I would be met with blank stares.

I’m also going to try to order a Bluetooth battery monitor to test this theory out myself.

 

Sorry to necro-bump this thread but I also have a 2024 Tucson PHEV with similar issues.

@tkenopic - since you seem to have the most experience with our cars, I would love your perspective on the above situation.

I think keeping threads like this open keeps it the topic organized and up to date. Your situation sounds really strange. I'm no expert, but do have experience with batteries on both this vehicle and my sailboat. One thing about Lead Acid batteries is that they do not tolerate full discharge very well. Remember the starting battery on the PHEV is Lead/Acid in the trunk. It is not just a 'compartment' of the Li-ion battery like it is on the HEV. What this sounds like to me is that the lead acid battery was fully drained at least once, perhaps multiple times before this issue, perhaps even before you owned it. By draining it all the way, it can quickly 'kill' even a brand new battery. I would definitely take it to the dealer for a couple of reasons:
1) It should still be under warranty
2) If/When the dealer can't figure it out, they should escalate the service request to a higher level
3) They should be aware of, and finding a solution for, this fairly common problem so that we don't need to buy an after-market battery monitor etc.

 

TomD New Tuscon Hybrid, 600 miles. Tried to start car this AM. The car was dead - no lights, no dashboard, no engine. Called service. Informed to press "Reset Battery" button on to left of steering wheel. I was told Reset Battery button would have to be pushed if car had not been used in the last 24 hours. It worked. Could not find any information about this very important issue Hyundai Manual. If I had been in the boonies (lots of boonies in New Mexico) and no cell service, I might still be there

 

You didn't look hard enough! Manual clearly explains it.

 

I bought my new 2023 Tucson PHEV in August and love it except that I've had to have it jump-started 6 times! Yesterday I spoke with a different service manager who told me that there are so many electronics that the battery can drain in 2 days if not driven more than 8 miles to recharge it. I work from home and don't drive every day. In other words, draining the battery is not surprising! He told me to consider a battery tender.

I would appreciate advice on the best battery tender that would be appropriate for this model car. Also, can the battery tender be left in place while driving -- or do I have to unplug it to go out and plug it back in when I get home? I am planning a vacation for later this year and wondered if I can disconnect the battery so it won't drain while I'm away.

Thanks for any info-
Susan

 

I bought my new 2023 Tucson PHEV in August and love it except that I've had to have it jump-started 6 times! Yesterday I spoke with a different service manager who told me that there are so many electronics that the battery can drain in 2 days if not driven more than 8 miles to recharge it. I work from home and don't drive every day. In other words, draining the battery is not surprising! He told me to consider a battery tender.

I would appreciate advice on the best battery tender that would be appropriate for this model car. Also, can the battery tender be left in place while driving -- or do I have to unplug it to go out and plug it back in when I get home? I am planning a vacation for later this year and wondered if I can disconnect the battery so it won't drain while I'm away.

Thanks for any info-
Susan

Definitely something fishy. My 2022 plug in has sat for weeks without issue. That said, both Nocco and Battery Minder make high quality trickle chargers. A battery minder is used 24/7 on my motor home when parked at home.

 

You can remote start the car from time to time unless garage is attached to the house. But yes you’d have to disconnect battery tender each time.but something still sounds fishy. So every car on the lot for sale will have a dead battery ?

 

Definitely something fishy. My 2022 plug in has sat for weeks without issue. That said, both Nocco and Battery Minder make high quality trickle chargers. A battery minder is used 24/7 on my motor home when parked at home.

Do you have to disconnect the trickle charger to drive the car? Which model is compatible with the Tuscon PHEV's 12V battery. I saw somewhere that it's an old-fashiond lead battery.

 

New 2024 Tucson PHEV

Just had 12v battery replaced under warranty at 3300km.

Obviously the battery should last longer than 3300km. Approx 4months, normal usage. Dealer felt we just had a bad bat.
On the plus side, dealer very helpful, warranty worked, yay.

On side note, manual says I should have a MFL68LDIN 37110-30540, bat number was under the retaining clamp so I don't know exactly what I in fact had.
Dealer replaced it with a E3711-0648MF, which as far as I can make out has identical properties. (600cca, 68Ah)
So I guess there are a lot of different bat parts/numbers that work?

However began monitoring the bat more closely. Within a week, new bat voltage dropped from 12.6 to 11.2. Then a long road trip recharged it back to 12.6.
But that week represents one fairly deep cycle, not the sort of thing a lead acid bat will take forever. As we speak I have a bat charger on the bat as it has dropped to 12.3v again.

Have ordered a clamp on current meter, will be taking measurements of what kind of loads a parked TucPhev puts on the 12v.

I already know that driving, EV or ICE, charges the bat, as does charging the phev.
I suspect just sitting there the load is higher than ideal.
I charge the PHEV at night when electricity is cheaper, and I suspect that siting plugged in waiting to charge, or after a charge, loads may be higher still.

Question remains is my car acting that same as everyone else's or do I have a hidden light on somewhere.

 

It isn't - or wasn't a Lithium Battery 13.8 KWH? I thought I read this is a reason why a Lead acid isn't used? Many reports of the Hybrid having the 12V battery drop some while sitting yours seems excessive.