I have noticed lately when I start my 05 trailblazer (4.2 68,000 miles) the volts are around 10 or 11 when I start it (been doing this since it has been about 30 degrees or below outside), but after about 3 seconds they jump up to 15 or 15.1 and after 30 seconds or so they settle back down 14 or right around there. I have a scan gauge so I always watch them. Is this normal or is there something I should check out?