We're using the 1800 mAh battery from the Samsung Epic Touch 4G, not the Samsung Galaxy...I ordered an external battery charger for a Galaxy assuming it would charge Focus batteries. It doesn't and the Galaxy batteries do not work on the focus but if you try to hook up a charger or connect to Zune it goes into a constant reboot loop.
Edited my typo
here's a link. This works in the Focus for sure: Amazon.com: Samsung Epic 4G Touch 1800 mAh Standard Battery: Cell Phones & Accessories
