Batterylight and brake light on startup

The battery light and the brake light remain on briefly (after all the other dash lights have gone dark) on startup after the van has sat for a couple of days. I suspect the battery is going bad. If I drive the van frequently, I don't see the lights but it's only happened twice.

Anyone else seen this as a sign of an impending disaster? Tell me it's not my alternator. I had all the oil leaks fixed.