I've been reading posts on the mbed forums, and I'm under the impression that I need to attach a coin cell battery holder to the underside of my FRDM-KL25Z. But is there anything else I need to do? I've tried powering the board through the VIN and GND. It does not power up using a coin cell, but does power up when I connect a 9V battery to VIN and GND. I'd prefer to use a coin cell, because that's much lighter and smaller, and I could attach the battery holder to the board.
Any help would be appreciated. I'm not an electrical engineer :-)