Datasheet

CR1220 12mm Diameter - 3V Lithium Coin Cell Battery

PRODUCT ID: 380

https://adafru.it/em8

$0.95

IN STOCK

You MUST have a coin cell installed for the RTC to work, if there is no coin cell, it will act strangely and

possibly hang the Arduino when you try to use it, so ALWAYS make SURE there's a battery installed, even if

it's a dead battery.