Q. I recently installed an aftermarket USB port with a digital voltage display in my newer Ford truck. I noticed my battery voltage varies significantly, between 12.9 and 14.1 volts, with no alternator warning liught on my dash.
Is this a sign that my alternator is failing?
A. Not necessarily. On modern vehicles, charging voltage can be as high as 16 volts, and as low as 13 volts. And there are situations where your alternator might not be doing any work at all if your battery is fully charged.
In many of today’s cars and trucks, the function of the voltage regulator is managed by the vehicle’s ECM. Alternator output is very precisely controlled—sometimes down to the milliamp.
Why a New Vehicle’s Alternator Output Voltage May Change
There are a couple of reasons why. First, the accessories and sophisticated electronics in late model vehicles place tremendous demands on the electrical system. Increased alternator control helps meet those demands.
Another less obvious reason is fuel economy. To reduce the parasitic drag of the alternator on your engine’s accessory drive system, the ECM may increase charging output during coasting or braking. This reduces the need to power a heavily-loaded alternator while accelerating or cruising. It sounds insignificant, but every little bit helps.
Finding & Preventing a Problem
But if you do suspect a problem, ensure contacts are clean at the battery, connectors, and grounds. Use a corrosion preventing agent when necessary. Connect a scan tool to monitor alternator output and look for battery and charging system fault codes.
Regularly test the battery’s health with a battery tester. If it fails, use the proper charger for your battery type, being careful to charge at a rate that will not overheat the battery. Retest the battery with a full charge.
Understanding New Vehicle Battery Management Systems
Also, many new vehicles now have a Battery Monitoring/Management System (BMS). If the battery is replaced in a vehicle with a BMS, a scan tool must be used to reset the system and enter the new battery information. The BMS manages batteries differently based on parameters like battery age, size, and type. Properly resetting the BMS will lead to longer battery life and better charging system performance.
I just add my own ground metal to metal.
Tim, you obviously know how important a good ground is for peak electrical operation at all times. A common mistake that is often made when upgrading components like an audio amp, the electric fuel pump or high capacity cooling fans that require higher current than the OEM component did, is the OEM ground wire needs to be replaced with one of a larger AWG (American Wire Gauge). Chances are that new component came with a larger AWG positive power wire and the negative wire must be the same size to avoid a current restriction and poor electrical performance.
Why do the all the lights flicker/fluctuate on my 2011 Challenger when driving. There is no change in flickering with a rpm change? I was told am need a new battery cause my present battery is 5years old.
Any thing to sell a batt. My 2000 convertible is on its second battery.
its not a every day driver. when new I installed a bat. maintenance float
charger keeps er at 12.5 vdc. The statement about ground straps is right
All our cars have added 8 gauge from negative bat. terminal to engine block.
Cheep insurance. Safety Fast !..