In the last month or so my battery light will come on from time to time after I start my truck when it's been sitting for eight hours or so. It only comes on for a minute or two and then go out and it doesn't do it every time. According to my Edge Insight CTS, my voltage is 13.6 to 14 but I've been checking my FICM voltage with it and for the first five minutes or so of driving it's down around 43 to 45 volts and then after it warms up some it's between 46 and 48 volts. I took my alternator off and took it to an Autozone and an O'Reilly's and both couldn't test it because supposedly the electrical adapter was bad. So do you guys think it's my alternator going bad? What else could be causing this?