Lately I've been getting the message in the photo below, "Low Battery, Convenience Functions Temporarily Unavailable." Along with that, the dashboard clock keeps adjusting its time. Could it be as simple as needing a new battery? And if so, which one? The car starts and runs fine, but I understand that there is a second battery in the engine compartment. Is that battery for accessories? Right now, I don't have the Comand Unit to include radio, navigation and satellite. Thanks.