Confused. so, if a baby swallowed a toxic button battery that burnt holes in gi tract, how would it be possible to not see symptoms 1 wk post ingestion?

Not that common: Button batteries are bad because the electric current does cause chemical burns in the GI tract. However, it usually only happens if the button is stuck somewhere. If a button keeps moving around and eventually out the anus, there may be no symptoms. Batteries that don't get stuck in the esophagus (and cause burns) usually pass through without burning any holes, but doctors do follow-up carefully.