I "retired" the EFB battery in my wife's 2015 VW Polo yesterday, really it was not (yet) causing me any big problems, but, as I have a 12V DC digital voltmeter thing plugged into the 12V DC Power socket, I could see that it was taking a very long journey before the indicated voltage was dropping down from 14.89V, so, as I had prepared for an early failure back in maybe late 2022, I considered that I'd be very silly if I waited until I had a problem with the original 59Ah EFB, and going by the chatter on many VW Group owners forums, it sounded a lot like that original EFB was slightly undersized and also not going to last much beyond the 7 year mark. So a few years ago, I bought a 70Ah AGM battery and have kept it "topped up" every 3 months while it was waiting to get used. For that car, annoyingly, I also needed to replace the battery tray and the thermal blanket, so now everything has been fitted to the car along with coding the battery management system to suit that change. I have never ever been in the situation where I felt that the battery capacity was really a bit low for that car and the way that we use it, so based on that experience, I'm sure that I've just wasted the extra money buying the next size up battery, tray and thermal blanket. Changing from EFB to AGM was also, for me unnecessary, but it has now been done! That was just my experiences nothing more.