If your iOS device appears intermittently in the battery list in the Battery Check, you may need to adjust a setting in iTunes. With the iOS device connected to your Mac, click on the device's icon in the iTunes window, just below the play/pause button. Once the device summary appears, scroll down to the options section of the summary view. Check the box next to "Sync with this iPhone/iPad over WiFi." Having this setting enabled allows the iOS device to stay 'connected' to your Mac when it is physically disconnected, allowing the Battery Check to provide results with the iOS device disconnected.