A failing battery will begin to show symptoms before failing all together. This car has a smart battery harness. If the computer senses that the battery is no longer outputting the voltage or amperage it begins to shut down “non-essential” operations. For example you may notice that the rear defogger stopped working, or the climate control fan is no longer working on the higher settings, or the dimming mirrors stop dimming. If this happens you’ll likely need a new battery, any auto parts or service center can check the charging system. You can replace it yourself but will need an OBD II device to “re-register” the new battery so that the computer recognizes it.