The serpentine belt jumped off when I crashed through a puddle.
No big deal to diagnose or repair. A new belt has already been installed.

But here's the thing: The battery warning lamp doesn't come on when the alternator's not turning. Only when I first turn the key.

Suggestions? (other than "Install an aftermarket voltmeter")

1999 Grand Caravan, Mitsubishi 3.0-liter engine.