The following website has a useful button battery algorithm (thanks to JL for forwarding this link):
One important point is that in an asymptomatic patient, a button battery in the stomach can be left alone if no coingestion with a magnet. If gastric battery is > 15 mm and child is less than 6 year, the recommendation is to check xray in 4 days and remove if still in stomach or whenever there are symptoms.
Of course, a button battery in the esophagus is a true endoscopic emergency. Recognizing that it is a button battery and not a coin can alter the outcome.
Related blog links:
Another link on foreign bodies, 2011: Postgraduate Course Syllabus – Slides, only – NASPGHAN.org (Look for the slides from Marsha Kay)