The Coin Board is a simple Coin Cell Battery holder board for Lithium (CR2032 Batteries). It was designed to be compatible with the Platform Board.
Note that the power path is interrupted by the two pins with the label "Switch".
These pins can be used as a physical switch to kill power to the project or as a convenient way to measure the average current draw, which is especially useful for low power designs.
More information can be found at http://www.kevindarrah.com/wiki/index.php?title=CoinBoard