Magic Keyboard not showing Battery Level in Bluetooth menu or preferences

Just bought a new Magic Keyboard for my iMac 27, running Yosemite (long story, stuck with it for a while because of having to use stupid Quark for some of my clients). This is replacing my trusty wired Mac keyboard that finally bit the dust. I understand some functions of this new keyboard won't work with my older OS, and can live with that. But the battery level is not showing anywhere, not in the Bluetooth menu or system preferences or anywhere else.

Help! I feel it's important to know if this thing is charged adequately. Is this keyboard defective, or is the problem Yosemite incompatibility?