What's going on with my 12v battery? Why does it keep dying? Could it be related to anything specific?

I’ve just had my (stock) battery die again for the second time. It’s really cold where I live, so that could be part of the problem, but it still seems strange.

I’ve had my 2023 Niro PHEV for about 16 months now, and it looks like I have to jumpstart it every 6 months.

I’m curious – I don’t often use the gas engine, maybe once or twice a week. Does the alternator only work when the gas engine is running or is there something else going on?

Do you use the accessory mode sometimes? That could drain the battery really quickly.

zabeen said:
Do you use the accessory mode sometimes? That could drain the battery really quickly.

Not sure if I’m following – what exactly is accessory mode on this car? I know in regular cars you turn the key to ACC, but not sure about this one.

@theresabostick
For push button starts, accessory mode happens when the start button lights up red, like when you press it without stepping on the brake first.

My 12v died when I went camping. All the opening and closing of the door with the lights on drained it really fast. Other people have mentioned the same thing. It can be fixed quickly with the reset button.

But, the reset button is only for the HEV, not the PHEV.

@Rowen
The reset button only works for the HEV.

OptimaPrime said:
@Rowen
The reset button only works for the HEV.

Oh, got it. Thanks for letting me know.

Rowen said:

OptimaPrime said:
@Rowen
The reset button only works for the HEV.

Oh, got it. Thanks for letting me know.

It would have made more sense if they used the reset on the PHEV too. I only had to use mine once, the day I picked it up. It had been sitting on the showroom floor for a while, and the battery probably died from the doors being left open or the lights being on.

I have a 2022 Kia Niro PHEV. The traction motor charges the battery. This has happened to me twice in the first year I owned it. The first time they jumpstarted it, the second time I had already bought a small Lithium-Ion jumper. It’s been fine for over two years now.

I don’t really understand why it happens. Running the gas engine doesn’t seem to help. Both times it happened in winter when the engine would run to warm the cabin. I’ve gone for a month without using the gas engine and had no issues.

It’s just one of those quirks with this car, like it happens with other cars too. Electronics are really sensitive, so battery protection is super important. I’ve even had to jumpstart a couple of Teslas for the same reason.

@susanbauer
My 2022 PHEV had the same issue until a recall updated the software. After that, I haven’t had any problems. You might want to have a dealer check if you have the latest version.

Following… I have a 2022 PHEV. The 12v battery goes flat after just 2 minutes of being in accessory mode. I probably need to replace it. The dealership is going to test it soon.

I have a 2019 PHEV. I had the same issue because I kept my dashcam plugged into the USB port in the centre console. Even though the camera was off, it was still drawing enough power to drain the battery. Now, I unplug it, and it seems to work fine.

Also, if the Auxiliary Battery function (can’t remember the exact name) is used too many times in a row, it stops working. It tops up the 12V from the main battery.

I think the 12V battery also gets used whenever the car communicates with the server for app stuff. Not sure if this is what is causing your issue though.

@maryschultz
I don’t have anything plugged into the USB (or tied into the fusebox, like a dashcam). I’m not really sure what this Auxiliary Battery thing is.

theresabostick said:
@maryschultz
I don’t have anything plugged into the USB (or tied into the fusebox, like a dashcam). I’m not really sure what this Auxiliary Battery thing is.

Here’s some more info about the Auxiliary Battery Saver mode: https://ownersmanual.kia.com/docview/webhelp/doc/a6b84de0-c1e6-4dc2-993d-c94c658f5bb1/topics/chapter1_12_8.html

It happened to me a couple of times with my 2024 PHEV Niro, about two weeks apart, right after we got it, but it hasn’t happened again. We got a volt gauge just to keep track of it, and we make sure to use up the electric charge before driving the gas engine every few days.

Some people think it’s not a real issue, but others seem to experience it regularly.

@Lilyharper
I should probably start running the gas engine at least once a week to be safe.

Not sure if this will help, but for my older HEV, I used to have the same issue because of human error. I wasn’t used to the engine being so quiet, so I would walk away without turning it off and the headlights would stay on.

If I press the lock button when I’m a little distance away, nothing tells me the car is still running with the headlights on.

@Cruise
Does your car not beep at you if you walk away? I always walk away with the car still ‘on’, but it beeps at me, and I have to go back and turn it off.

Got a low battery warning the day after I set up the car to schedule charging for the next day. Not sure if it’s related.

2024 Niro PHEV

I read somewhere (maybe here) that the charging circuitry draws power. This could be why I get a ‘Battery Saver’ alert if I leave the car plugged in over the weekend. If I unplug it when charging is finished and don’t leave it plugged in for a couple of days, I don’t get the alert.

If this is true, then the constant parasitic draw against the 12v might be what’s draining it.