the charging cycle is temperature related . a cold battery does not charge very well, below 45 degrees mine stays at 14 when it gets to 60 it will stay just under 14 and when it get to 70 and above it will always be just above the 12 volt range. i think gm does this because the hotter the temperature the faster the chemical reaction is in the battery which makes them sulfate and boil of the chemical in the battery which shortens the life of the battery