Battery Voltage Rollercoaster Unraveling the Mystery During Drives

I got in the car. Checked voltage before and after starting It. Voltage hits 13.7 volts for a breif second after starting then drops to battery ... Ford has a battery management controller in these vehicles these days, and because it is running an AGM battery rather than the traditional lead ... Does so at idle or while driving down the road. Tail lights ... I placed volt meter on the battery and showed him the voltage fluctuation. Get the battery load tested. Only way to confirm battery is indeed good and not having a weak cell only holding a ''surface'' charge. This is a battery maintenance function, not a electronics operation function. When batt needs more charging, ECU commands (regulates) alternator to meet that ... It is highly likely that the alternator and/or voltage regulator are the problem. '04 330i ZHP - OEM Clears - ///M Strut bar - CoolantSnitch. The fluctuation happens when parked and driving while increasing engine RPM's. ... First check all the wiring connections to the alternator ... It sounds like the voltage regulator inside the alternator is bad. Just an FYI most all auto parts stores will test your alternator, battery, ... After 10 minutes or so of driving, the voltage of the battery will drop and hover in the range of 12.2-12.5. There are 2 ways is raises back up. it is normal. THe computer controls the alternators output. (to save gas). THis is based on the batterys charge, temp, and vehicle electrical ...