Replaced key battery and now fob not working

[OllyKBY23]

Hi, I have had the key battery low message come up on the dash for my main key (normal VW group flip key). Instead of replacing it I just used my spare key. Then my spare key battery became low and the same message came on the dash. I bought replacement CR2025 batteries for both keys. I firstly changed the main fob, making sure its fitted correctly and the right way up, however it now does not work. I reinstalled the original battery and now that does not work with the central locking. It previously worked on central locking with a flashing red light, I only changed it because of the low battery message. There is no flashing red light on the fob but it will still start the car in the ignition barrel. Is there some sort of timer before the key loses a code or programming that needs to happen after a key battery replacement? However, it looks to me that the fob has actually decided to give up as there is no flashing red light.

I am a bit hesitant to change the battery in the other key now in case that decides to kaput? Please advise if its just a simple battery change and I will go ahead with changing the other one. If not should I book it in?

 

[DEAN0]

Just a thought but have you removed the protective film from the new battery ?

 

[SRGTD]

@OllyKBY23 - as @DEAN0 has suggested; quite a few people on various forums I visit have been caught out by this.

Alternatively if you bought your new batteries online, unfortunately it does increase the risk that they might be poor quality copies of well known branded batteries, in which case it could be the batteries are at fault.

With batteries I tend to buy mine locally - usually from the local Screwfix. Any I’ve bought from there have always been problem free and they’ve had a very long shelf life, and if there were to be a problem with them, buying locally means I can easily take them back for an exchange or refund.

 

[cairus]

I installed VW Group keys from experience only VARTA batteries. Even there are problems now and then. But by the time I get the second new one it's working again.

 

[MarkDH]

I've very recently replaced both of mine. Used Duracell batteries ordered from Amazon. Had no issues.
The old battery was removed and the new one put in within 10 seconds. Don't know if that makes a difference.
2018 FR TSI 1.8 DSG

 

[WozzaB]

I had the low battery warning pop up, put a new battery in and the warning was still there, after a quick Google I changed the battery in the spare key and had both near the car and the warning went.
So replacing both batteries and letting the car sense both keys worked for me.