I had a similar experience recently with Elmhurst Auto Cllinic. I purchased a new battery from them, and when they got the car in the shop they told me that not only was my old battery weak, but I also had a bad alternator. Since I have an extended warranty on the vehicle, I immediately took it to the dealership. After thoroughly checking out the electrical system, the dealership advised me that the alternator was perfectly good. There's a definite pattern here.