I never owned a hybrid so this may be irrelevant but on a standard ICE car the alternator may not be charging the battery. Typically the battery starts the car and the alternator charges the battery and runs the electrical system. If there is a way to have the gas engine run to check if there is more voltage going to the battery while the engine is running vs when it is off then that would be the first thing I would check. If you take short trips, running the car on the gas engine at highway speeds for about 30 minutes the battery should be fully charged; I tend to try and run it a bit longer (45 minutes).

Apparently the new battery technology (AGM) is less forgiving than standard lead acid batteries and if the charge gets too low the battery shorts out.

Not sure if any of this applies to your situation but it may.

 

Thank you for this. After jump starting and going on a run for 30 minutes or more the car is fine and performs as it should so I am assuming the battery is getting charged from the alternator ; but then often the day after there is not even enough power to unlock the car

 

See the existing discussion on this issue below

https://www.hyundai-forums.com/threads/2025-tucson-hev-12v-battery-needs-to-be-reset.717897/unread

 

Don’t leave your car key near your car

 

FWIW, I have my key fob ('24 HEV) hanging on a wall just inside the door from the garage, less than 10 ft from the vehicle and never have an issue. Granted the wall does provide some isolation but...

On the other hand, my BMW Z4's fob also hangs there and it'll sometimes wake up when I grab the fob for the Hyundai, different technology and software I suppose.

 

Your car must have a big parasitic current draw. You need to start puling fuses to find the circuit that is causing the draw. Take a pic of the fusebox then take a bunch of fuses out till you narrow it down. On such a new car the dealer should be doing this work under warranty. Have you checked at night for a light on like the glovebox etc?

 

What’s confusing me most is that you said you paid the dealer $175 for a new battery, a part that doesn’t even exist in your ‘25 hybrid. Recommend you have some heavy discussions with your dealer. You shouldn’t be paying for anything to service your brand new vehicle.

 

I totally agree!

 

Don't they have a 12 volt accessory battery for cranking, lights etc?

 

Yes for lights and accessories but not for cranking, and would cost a lot more than $175 to replace. It would also be a warranty item.

 

I have a new 2024 Caligraphy Hybrid and there is a battery in the rear cargo area. And with 1350 miles I woke up to dead battery yesterday in a hotel parking lot while on vacation. Key fob's as well as phone app wouldnt work. Even worse, the "key" that is supposed to unlock the drivers door would not even go in the slot to do so. Call Hyundai and they sent someone out who was able to get in using tho old hook method to open the drivers door and then we were able to jump it to start. Today, started with no problem.

 

My '18 Elantra has an electrical "closed" rubber pushboot activated by the rear door which was knocked off causing the interior lighting to stay on. Battery drained and dealer took four days to enlighten me on this pushboot in my unfamiliarity with this accessory on this new purchase. Had another installed and was on my way, the factory battery began weakening at four years causing slow starts which was replaced with a German manufactured WalMart Everstart Platinum having a 5-Year warranty.

 

I'll repeat what I've said in another post...

Everyone needs to temporarily remove the Battery from their FOB and go through the exercise of manually unlocking the door and then starting the vehicle by holding the FOB against the Start button. Do this once soon - before you have to do it in the dark or when in a big hurry. It is not a simple or intuitive process. Thus, it needs to be learned when not under duress.

Also learn where the reset button is on models that have them.

 

I find people that always rely on key opening may end up finding the key barrel frozen when it's finally needed in an emergency.