 Because if you test it at the battery, maybe you're getting a good connection there, but you're not to the rest of the car. So if you verify that, then somebody's going to have to hook a scanner to it and see what codes come up. And if you've got a security code, you might need to do some relearning before the car will start. And some of these even have a battery change mode where you plug a scanner in. You say, I'm changing the battery. It'll say remove battery. You remove it, put the new battery in.