Well, it really depends on some factors.

1. What was the original life (charge) in the battery that was inserted?
2. How often do you use the push buttons on the key fob versus the passive NFC (fob in car) to start the car or unlock the door when you are walking up to it?
   1. Pressing a button transmits a RF signal that is hundreds of times more powerful and battery draining than the NFC connection.
3. How often do you take the fob with you when you park the car in the garage versus just leaving it in the car. Taking the fob out of range will cause the fob to stop communicating constantly with the car. Leaving it in the car keeps the NFC connection open and the car always knows that the fob is there. Albeit a smaller drain than pressing and/or holding down a button, it's still a larger drain than having the fob out of range and going to sleep.

So, how long should it last? Your own personal use will determine that. But I would say that at least a year and a half to up to 3 years is a good target zone.

 

Generally they should last a few years at least. As @Bookworm has said, there are a number of factors involved. The latest (2021 onwards) keyfob shuts itself down after a few mins of not moving, and if you put it into a faraday bag, it will communicate less.
The car will inform you when you start if the keyfob has low battery, so it's probably useful to use both keyfobs from time to time to check them.
Once you get a low-battery alert you would have a while to change it, so it's not as if you need to have a spare battery around.

Murphy's law though - if you mainly use one keyfob, when it goes flat, you will likely find that the other keyfob has a flat battery too.

Lastly - if it goes completely flat, you can pop the key out the back of the keyfob to unlock the door, and start the car by pressing the silver part (key part) of the keyfob against the start button to start the car.

 

and start the car by pressing the silver part (key part) of the keyfob against the start button to start the car.

I thought it was the other end, the silver bit with the light in it.

 

Beyond 12yrs for me.

 

In a proximity key? Doubtful. 2-3 years is what I've found with 4 cars having proximity keys.

 

Use only genuine Duracell or Energizer batteries. 'No brand' alkaline ones will last you only a few months. As other mentioned, the fob may keep 'talking' with the car when it's parked at home - keep the fob as far away from the car location - i.e. not by the door near the driveway, or keep it inside a faraday bag and make a test for the bag, try starting the car with the bag near the start button.

 

We are still on the original 2014 FOB batttery!

 

What? You waiting on an AD to get it changed out?????

 

The best batteries for fobs have always been Panasonics, in my experience. And that's what I use. The main reason was the others' surface wasn't liked by fobs, but I'm sure they're better now, so it probably doesn't matter anymore. But just wanted to mention it . I typically replace the batteries every 2 years, just to be proactive. Still have several that have to use before they expire, hence the practice. But as mentioned earlier, the car actually tells you that the fob's battery is low, so it's not necessary.

 

I've replaced mine twice in the fob I use the most (the other spare is just sitting in the house and rarely gets used) and replaced that one once. Vehicle is 6 years old (well in a few weeks). In my old 2005 Chevy Equinox POS (which was NOT proximity based), I think the fob battery lasted close to 10 years, but that was not a PTS or proximity fob.

 

I have an alert on the bluelink app that just says "Smart Key Battery" along with "washer fluid". I'm certain that the washer fluid isn't low.. Not sure about the key battery if its really low or anything, but my key is usually pretty far from parking lot that I tested it cannot communicate with car (lock /unlock).

 

there is no alert, on your bluelink, the alert is off, only when the alert is on then your washer or battery will be low

 

Thanks! Strangely, I haven't seen this "alerts" slide before on the app and just few days back, I noticed it. I just checked my online account now and I see additional tabs under alerts, they are off. I think i'm good. Just bad background colour to show the alerts into.

 

I don't have that screen nor anything on fob battery and washer fluid!????? I'm on Android though.

 

I don't think it matters; it's close enough that either side should work IMO. By the way, I have a key card hidden that I'd use if something happens to the fob. It was pretty cheap at $30, so I recommend getting one. It's a shame my 2023 G70 2.0T SP doesn't have that feature. The 3.3T SP I returned did, so hopefully in a future software update. We'll see.

 

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Key cards also require a Card reader (mounted on door) as well.
Just fyi...

 

Key cards also require a Card reader (mounted on door) as well.

The car either comes with that feature, or it doesn't. My Calligraphy does... but it didn't come with a key card; I had to buy it separately for 30 bucks. But it's easy to program: Just put the key card where you charge the phone wirelessly, put both fobs somewhere in the car, select 'key card' from the vehicle settings menu, then scroll down and hit 'save'. And done. I tried the ignition with fobs away from the SUV, and it worked, but didn't try it to lock the vehicle. I leave it hidden inside the SUV, in case I lose the fob, so no need to open the doors anyway; I'd do that with the phone app. Wish my 2023 top-trim 2.0T G70 came with that feature, but it didn't (only 3.3Ts).

 

They same as flash light battery,, the more you use it, the more life you take out of them..

 

Can you make two key cards for one car or only one is allowed?

 

Just one, I was told, but not sure about that (good question). Only one way to find out (ha ha). But my guess is a 2nd card would just delete the 1st one, rendering it useless. Once programmed, it's permanently linked to that vehicle; it cannot be used on another vehicle. So 1 key card per vehicle.

 

I’ve had batteries in my FOB(s) last from 1 year to 5 years. Always replacing them with “Energizer’s.”

 

After four years and 8 months (31k miles) both key fobs batteries are dead. No warnings on car display like my old car (2014 Kia Optima) did- “Key fob battery low” on car display. No welcome lights and you can’t opened doors.

 

These are not a HYUNDAI key fobs but my wife's VW 2011 lasted 8 years before they needed to be replaced. For my Ram truck bought new in Nov 2007, I am still using the original batteries in my key fob, 16 years.

The Hyundai are only three years old.

 

My key fob battery lasted only 4yrs, I rarely used the buttons, I placed fob in faraday bag on the weekends.

 

The key fob battery lasted 4.5 years on my 2019 Santa Fe Ultimate. There was no low-battery warning message. I went to start the car and it said "key not detected". I could start the car by pressing the start button with the key fob.

 

Same thing happened to my wife, but she was out and couldn't get the car unlocked with the fob

 

There will be telltale signs when the key fob battery is weak. For me, it was unable to unlock door on the 1st time, it eventually unlocked after a few more presses on the door handle button. This unlock inconsistency persisted for ~4 days, then decided to change the key fob battery....and problem fixed.

 

hi here i have a hyundai elantra sport 2018 tech package and my first battery last like 3 years and after that like 1 year and a half but in the last year or so i need to replace battery every 3-4 weeks.. always used good energizer one replace my key fob with the other spair that i have tried faraday bag to keep the key in it nothing seem to solve the problem any idea ?