[maples37]

> Your car will come to a stop on it's own when there's no electrical power left.

Newton's laws would disagree. "An object in motions stays in motion..."

GP is asking "what happens if the alternator dies, and the battery runs flat while you're driving?" This may sound like an outlandish scenario, but my uncle had something similar happen to him not too long ago.

And not all cars can run solely off the alternator when the battery is dead. Several years ago, my mom's Grand Caravan wouldn't start when she was out. She called AAA, and they jumped the car, and it started just fine. But as soon as the AAA guys disconnected their jumper pack, the van died. They tried it several times and weren't able to get it to stay running.

If your brakes require a fully-functional electrical system to apply any force at all, that seems like an unacceptable failure scenario.

[BenjiWiebe]

To be a real emergency, it would have to also happen when you were planning on braking very soon. At least with my driving patterns most of the time I'm driving I'd be able to safely coast to the shoulder. The failure would have to coincide with a stoplight turning red or something. Hmmm, even the horn wouldn't be working without electrical power...