My 91 850 voltage is registering at 11.75 when idling. Should it be up to 14.00? I just replaced both batteries. The mechanic says it is the alternator going bad and that could possibly be causing the car to jerk a little at 55 mph. Could this be true or is there something else I need to check? What happens when the alternator is not at the right volts? Would it cause some jerking? Any advice and help will be greatly appreciated. Thanks for your help and time. 91 850ia (58k)