Datasheet

CR1220 12mm Diameter - 3V Lithium Coin Cell Battery

PRODUCT ID: 380

These are the highest quality & capacity batteries, the same as shipped with the

iCufflinks, iNecklace, Datalogging and GPS Shields, GPS HAT, etc. One battery per order...

http://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.