My car was running sluggish. Cut out on me a few times at the traffic lights. It's fine when it's going, but idling is rough, and slowing down to a stop is where it's most likely to cut out. Took it to a certain department store's auto center for fuel system cleaning. As they finished up, I was told that the battery died. I had just replaced it a few days earlier, so I asked for an explanation. They suggested that I have the charging system tested. So they did, and told me the alternator was bad. They replaced the battery and alternator. It's running a little better now. Barely. So after spending over $500 there, I returned to the store where I bought the battery. They tested it and said it was fully charged. The manager of the auto center wasn't available yet, but I don't know what kind of explanation to expect, and what I can do. Any suggestions?