Seat Leon III - After replacing the battery in the key, the car reports a low battery in the

Hi.

I would like to ask for help with an unusual problem. I have recently replaced the CR2025 battery in my key (Seat Leon III 2016) with a new Energizer battery:

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Battery marked "fit for purpose" until 2026 so looks like a fresh supply. The problem is that 3 weeks after replacement, when starting the car on the computer a message pops up to replace the battery....

I measured the voltages and yes, there is a Panasonic battery in the other remote (spare). The voltage measured with a meter on the battery is 3.01 volts.
The battery in the key fob (Energizer) is 3.05 volts, I checked after pressing the button for example - 3.02 - 3.03 - a marginal drop.
I checked the 2nd battery from the blister (when I bought it there were two for replacement). A new unused battery has a voltage of 3.23 V.

Now to the question:
What could be the cause of the battery being identified as used despite the correct voltage? Could the fact that the new battery was 3.24 volts have messed up the electronics in the key, or switched something and now anything below 3.2 volts is reported as too low a voltage? As I mentioned the spare key has a weaker voltage and it is not identified as a battery to be replaced. Please help to unravel this conundrum.

Check the contacts in the key (cleanliness) through which the battery connects to the rest of the electronics, as a voltage drop can be deposited on them, which can cause the battery to be treated as worn out.

Hi, I have tried this unfortunately nothing has worked. The contacts look perfectly clean. I also did the trick of taking the battery out of the key for 5h. After putting it back in, the key reported no battery problem for 2-3 days then the problem returned.

Maybe something is wrong with the antenna in the key. Do a test from what distance it stops "catching".

To me, this 'number' would indicate that current is escaping from the battery as it is in the key minimum and this is causing the voltage on it to sit and not have time to rest - when it was removed it had time to regenerate. If you can see nothing on the board itself, then the problem could be in any of the buttons that it is not giving 100% break.

As for the range of the remote - I think everything is fine - I am able to unlock the car from 20m away through a closed door in a building.
I'm going to do one more test - I'm going to reposition the battery from the spare key and see how things look. The original battery was a Panasonic CR2025.

It's not about the range of the remote control. I don't know, but I presume that the information that the battery is too weak is due to the fact that maybe the amplitude of the key signal is low, as a consequence of low battery voltage when the button is pressed. That the battery is under load not only when the button is pressed would be confirmed by an experiment with its 5 hour rest, after it was removed from the key. During this time, the unloaded one had time to regenerate and then run for three days.
I don't know if this is feasible, but I would try to check (measure) by how much the voltage on the battery drops when the button of each key is pressed in both keys.

gimak wrote:

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I don't know if it's feasible, but I would try to check (measure) how much the battery voltage drops when each button is pressed on both keys.

But it is feasible to check with an ammeter the current consumption of the remote control, it should be 0 mA, the consumption only when the button is pressed.

I checked the current consumption of the remote control with an ammeter and it is 0 mA. The consumption when pressing the button jumps to 1 mA.
Now a curiosity:
I swapped batteries: from the auxiliary key I put a Panasonic with 3.01 V into the key I use every day, and into the auxiliary remote control an Energiser which has 3.03 V according to the meter.
The car for both cases now reports no need to change the battery. I have also done the manoeuvre of taking the battery out of the primary remote - putting it back into the remote and yet the car still reports the need to change the battery.

I'll drive around in this configuration for a few days and let you know what came up, I haven't had such a case in any previous car yet. Perhaps I unnecessarily purchased a different brand of battery to the one that was in the remote control and this is the cause of the problems....

Part, a brief update after a few days of testing. It turns out that there is something wrong with the batteries I purchased after all. I mentioned earlier that I changed the batteries in the keys:
I put the battery from the spare key into the primary key, and put the one I bought new into the spare key.
I use the keys alternately and the result is as follows:
The primary key (with the repositioned Panasonic battery from the primary key) reports no errors.
The secondary key (with the new Energizer battery) reports a low battery error.

In my opinion, this clearly proves that the problem is with the battery and not the key electronics. I guess I was out of luck buying these batteries. Maybe it was some kind of stock lying around? Hard to say. On the other hand, it's better that it's a problem with the battery than with the key .

To me the batteries (two) in my Audi key lasted 10 years. Could be a fake Energizer or that's the quality of batteries they make now. In addition to the voltage, the internal resistance is important. The remote control draws current in, short pulses and then the voltage can squat (impossible to pick up with a normal multimeter). The circuit in the remote control monitors the power supply and, if it is too low, sends an appropriate message to the car about the low battery.

From my own experience, I know that replacing it with a battery from aso (made in china) helped. After removing the battery, press any button on the remote control before inserting the new one.

jacek074 wrote:

After removing the battery, press any button on the remote control -before inserting a new one.

And why is that?

balonika3 wrote:

jacek074 wrote:

After removing the battery, press any button on the remote - before inserting a new one.

And why is that?

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Because if you listen to your brother-in-law's cousin whose friend read somewhere that it helps, that's the way to do it.

I am not saying that the battery is ok. But for the appearance of this message there is a software update in bcm

In my case, I ignored the message on the display about the low battery in the key until finally the battery went completely dead. The voltage of the discharged battery was 3.01V. I had a Duracell DL2025 battery (same as CR2025) bought much earlier with a "best use before 2025" date. When I inserted it into the key there was no response to pressing the button, the red LED did not flash at all. The battery was showing a voltage of around 3.31V. I read up on various forums (English language) about this problem and mainly the problem of a weak battery came up. I also had a slightly thicker Energizer CR2032 battery, some people force it into the remote, I put it in just for a test and surprisingly the remote worked, voltage the same as the Duracell battery. Then I reinserted the Duracell DL2025 battery and it is already working without a problem, no coding was needed. I think that sometimes the electronics can get blocked in the remote control and such flowers happen. It is best to have 2-3 CR2025 batteries from different manufacturers in reserve.

bladykm61 wrote:

I also had a slightly thicker Energizer CR2032 battery, some people force it into the remote, I put it in just for a test and surprisingly the remote worked, voltage the same as the Duracel battery.
Then I reinserted the Duracel DL2025 battery and it is already working without a problem, no coding was needed. I think that sometimes the electronics can get blocked in the remote control and such flowers happen. It's best to have 2-3 CR2025 batteries from different manufacturers in reserve.

I had a similar situation recently with a remote control for a corolla. The battery removed from the remote from the non-functioning remote had a voltage of 3.02V, I figured it could still go. After putting it back in, the remote came to life, but for a very short time. So I removed the battery insert and moved the battery without removing it and the remote came alive again, so I thought the cause was poor contact between the battery and the remote's contacts. So I bent the contact plates and the remote came alive again for two days. I got tired of playing with it and replaced the battery with a new one and so far the remote is working, I wonder how long it will last. It seems that in remote controls at this battery voltage level the remote stops working.

patryko_88 wrote:

Partly, a brief update after a few days of testing. Turns out there is something wrong with the batteries I purchased though. I mentioned earlier that I changed the batteries in the keys:
I put the battery from the spare key into the primary key, and put the one I bought new into the spare key.
I use the keys alternately and the result is as follows:
The primary key (with the repositioned Panasonic battery from the primary key) reports no errors.
The secondary key (with the new Energizer battery) reports a low battery error.

In my opinion, this clearly proves that the problem is with the battery and not the key electronics. I guess I was out of luck buying these batteries. Maybe it was some kind of stock lying around? Hard to say. On the other hand, it's better that it's a battery problem than a key problem

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And how is the issue today? I have a similar problem, except that the LED has even stopped flashing in the remote control.

In many cases even brand new batteries coming directly out of the package which measure 3v and more with multimeter can not work in practice.Try to replace it using a different battery brand.

Batteries from different manufacturers, despite identical appearance and size, have different capacities and thus different maximum discharge currents. It would be a good idea to look in catalogues and choose a battery with better parameters than the one from Energizer.