My wifes car is comming up on 6 yrs old with the original battery. 2 weeks ago she told me that the car seem to turn over more slowly first thing in the morning than she had ever noticed,( 13 deg F at 6am). Since then everything has been fine with no noticable issues but, temps have been above 30 deg F lately. I checked the battery with my volt meter while the engine was not running and it read 11 volts. I compared this with my other 3 cars and they were all 12 volts(not running). Is this my warning sign that the battery is on its way out and that I should replace it before the temps really drop? Also, is 11 volts still a good reading from a battery?