So I replaced the battery on my 2018 Golf GTI last weekend because it was clearly struggling to crank in the mornings, and I thought everything was sorted until I realized that the start-stop system hasn't worked even once since the swap. I double-checked everything, the terminals are tight, the voltage looks good, and the car starts perfectly every time, but the little green start-stop light on the dash just refuses to come on no matter how long I drive or how many times I stop at traffic lights. I started reading up on this and apparently on modern VWs, the battery needs to be coded or adapted to the car's management system so it knows that a new battery has been installed and adjusts the charging parameters accordingly – something I had no idea about before I did the job myself. I found batteryzoneuae.com/volkswagen-battery-replacement which seems to mention the importance of proper registration for these cars, and now I'm wondering if I need to take it somewhere to get the coding done or if there's a way to do it myself with an OBD tool. Has anyone else run into this issue after a DIY battery replacement on a Volkswagen, and did you manage to get the start-stop working again without going to a dealer? I'm kicking myself for not researching this beforehand because it feels like such a simple job that's now turned into a headache. Any advice would be really appreciated because the start-stop not working is driving me crazy even if it's not a major mechanical problem.