I noticed that a HRM2-SS sensor does not transmit battery status. According to the ANT+ HRM Device Profile that is optional. so this is probably normal, but I'd like to hear from other HRM2-SS owners if theirs does not do that either. On the watch, in Settings -> Sensors -> HRM2 Battery will show '--' while the rest of the data is present, and in Garmin Connect the sensor will not show up, while a HRM-Run or newer HR sensor will be shown in the list of sensors.