2017 GT Premium - I have the volt meter pulled up and noticed when I am off the accelerator it's at 14 V but when on the accelartor it drops down to 13. Eventually it goes to 12.....now and then. Doesn't sound normal to me as every other vehicle I have ever owned had a steady 14.2 - 14.3 charge rate. Is this normal for the S550's or do I have a regulator or alternator issue?