Alternator replacement, and more reading
The third reason is convenience. Independent mechanics may offer a warranty on your car repair, but the warranty is good only at their shop. If you're caught away from home, what good is a warranty for a shop a hundred miles away? On the other hand, national chains cover the country, so you would have to be someplace exceptionally remote to be more than a short drive or tow from the nearest branch of a chain where your warranty is good. That can add up to considerable savings. You can also get personalized service at a chain just as easily as at an independent mechanic's.