I had the car in for Service A today. The main battery failed the load test, but I opted not to have them replace it at this time. It was 16 degrees (F) when I brought it in, so it was a "worst case" scenario and I just cannot bring myself to pay someone $90 to replace one of the easiest battery jobs around (now my Audi A3 3.2 with the battery under a panel in the trunk....THAT was a PITA every time I had to do it!). But, a battery replacement is definitely in my very near future.
SO, this probably answers my question about the Start/Stop still not working after replacing the aux battery (I hope).
It seems like there are aftermarket batteries out there with higher CCAs and better warranties, so I'd rather spend the $ on better parts instead of pricey MB labor. I am thinking of the Optima Yellow Top Deep Cycle Battery, Any reviews or recommendations, anyone? TIA!