Auxiliary battery in my Mercedes died – anyone know a good fitter near The Meadows?

I’ve had this ongoing issue with my GLE where the start-stop function stopped working a few months ago and I just ignored it because I figured it was some sensor glitch, but now the main battery is draining way faster than it should and the garage I took it to told me the auxiliary battery is completely dead and it’s been putting extra strain on the entire system. They quoted me an insane amount at the dealership, like seriously eye-watering figures that made me choke on my coffee, and I just can’t justify paying that much for what is essentially a small secondary battery that handles the start-stop and the entertainment system when the engine is off. I’ve been asking around the neighborhood here in The Meadows because a couple of my neighbors have similar cars and they must have dealt with this at some point, but everyone seems to have a different story about where they went and how much they paid. I found a place online that offers Expert auxiliary battery fitting in The Meadows, which would be incredibly convenient since I don’t have to drive far and risk getting stranded if the main battery decides to give up too, but I’m always nervous about trying new places without some solid recommendations first. Has anyone here had their auxiliary battery replaced recently and can tell me if the process was straightforward and whether the shop actually knew how to code the new battery properly? I’ve heard that if you don’t register it correctly the car won’t recognize it and the whole thing becomes a waste of money, so I really want to make sure I’m dealing with people who actually understand how these newer Mercedes systems work.