Watch Battery is a trinket added in the Afterbirth expansion.
- Increases the chance of a Little Battery pickup after clearing a room by 6.67%.
- Increases the chance of random pickups being a Little Battery by 2%.
- Has a 5% chance to add an extra charge to Isaac's activated item upon completing a room.
- AAA Battery: Watch Battery triggering after clearing a room will also trigger AAA Battery, provided the activated item was missing exactly 3 charges prior to clearing the room.