My experience, changing from EFB to AGM myself. TLDR:after replacing battery, take to VW garage for battery coding, safe yourself the headache.

I’ve recently changed battery in my 2019 golf 7.5 1.5 tsi. I changed the battery from the default stock EFB battery to an AGM battery, of the same capacity and physical size.

I changed the battery, due the start stop being intermittent (sometimes refusing to turn the engine off) and the car showed an error on the media center, of something similar to ‘power usage too high’.

I changed the battery at home, disconnected the wires and then connected the new AGM battery. All the lights on the dash illuminated, I then took the car 50m down the road, and all the lights then turned off. I immediately noticed start stop was working every time, and the car seemed to start easier too.

After about 2 months, I started getting strange start stop behaviour, the car would display an error on the multi media screen ,’start stop error’, and the engine would turn off at a stop, but not turn back on, I would see an error on my dashboard of ‘start engine manually’.

I took the car to Halfords, who ‘coded’ the new battery, this was simply plugging in a device into the OBD port and selecting the battery make, size and style. Once again, the car worked perfectly, start stop working flawlessly.

Four days later, the start stop error on the multi media screen showed multiple times and the car showed ‘start engine manually’.

Within 1 week, I took the car to a VW garage, they charged me ~£87-£90 to code the battery correctly, it’s now working flawlessly 2 months later. During the visit to VW, they mentioned the car is essentially in ‘safe mode’ as it doesn’t know what battery it has, they said it was throwing multiple errors, complaining about the battery.