[10mm]

So the info center says I'm running @ 12.5 volts

Is this a normal range while putzing around town ??

[DarkKnyte]

If it’s not 13.8v-14.4v I’d look critically at my alternator, or what aftermarket loads (such as amps, lights, etc) that I have installed.

[Alpha1BC]

This has been covered quite a few times on the forums already. Quick search for battery, voltage, or alternator should turn one up. This is normal behavior. The alternator is engaged/disengaged as needed depending on electrical load and battery state. You'll typically see anywhere from battery voltage of ~12.5 up to 14.5 V depending on electrical load at any given time. Only time you'll usually need to check the alternator is when you see the alternator/charging failure message on the dash.

[10mm]

Thanks Alpha, It has read as high as 14.3

Sounds good

[ember1205]

Originally Posted by Alpha1BC

This has been covered quite a few times on the forums already. Quick search for battery, voltage, or alternator should turn one up. This is normal behavior. The alternator is engaged/disengaged as needed depending on electrical load and battery state. You'll typically see anywhere from battery voltage of ~12.5 up to 14.5 V depending on electrical load at any given time. Only time you'll usually need to check the alternator is when you see the alternator/charging failure message on the dash.

Agreed. I've seen mine everywhere from right around 12.5 to about 14.5 and there seems to be no way to 'guess' what the reading might be based on circumstances. After starting the car multiple times without driving it or allowing it to run for more than 30 seconds or so, I've seen the gauge show 12.5. Other times, after having a battery tender on the car for days with a topped off charge, it will show 13.5 or higher right after cold start and while driving.

[Camaro fanboy]

yep same here
changes voltage at any time.

[Rock-It Man]

Go on a long trip, and the next day your voltage will be 12.5 for a while. Make many short trips or leave the car sitting, and the voltage will stay high to catch up on charging.

[10mm]

She was 14.5v at this mornings start up.

Pretty much knew there is variances in charging.
Always good to ask the hive 😁

[ember1205]

Originally Posted by 10mm

She was 14.5v at this mornings start up.

Pretty much knew there is variances in charging.
Always good to ask the hive 😁

There's a lot more to it than just charging, though. Combined with the fact that I'm not sure it's actually know what that reading is actually showing. It is alternator output? Voltage across the battery terminals? Voltage across another specific point in the car? Additionally, the fact that it isn't actually a mechanical gauge means that it could also be showing some sort of combination of readings from multiple areas in the electrical system.

[CamaroSSStlfan]

When I first bought my Camaro I noticed this too and was freaking out. Even bought a new battery as well, but everything checked out. These newer cars are more power efficient. My last car was a 2012 Mustang GT.

I made a post on this too when I first bought my car.

[nancygrl]

It's normal across all of GM offerings. Used to be called; "smart charging". Now "The new GM charging system is actually called the electrical power management system. It’s designed to monitor vehicle voltage and only charge the battery when necessary. GM does this to improve gas mileage and reduce the need to generate power when it’s not needed."

[ctrlz]

DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > ELECTRICAL POWER MANAGEMENT OVERVIEW
The electrical power management system is designed to monitor and control the charging system and
send diagnostic messages to alert the driver of possible problems with the battery and generator. This
electrical power management system primarily utilizes existing on-board computer capability to maximize
the effectiveness of the generator, to manage the load, improve battery state-of-charge and life, and
minimize the system's impact on fuel economy. The electrical power management system performs 3
functions:
It monitors the battery voltage and estimates the battery condition.
It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
It performs diagnostics and driver notification.
The battery condition is estimated during ignition-off and during ignition-on. During ignition-off the stateof-
charge of the battery is determined by measuring the open-circuit voltage. The state-of-charge is a
function of the acid concentration and the internal resistance of the battery, and is estimated by reading
the battery open circuit voltage when the battery has been at rest for several hours.
The state-of-charge can be used as a diagnostic tool to tell the customer or the dealer the condition of
the battery. Throughout ignition-on, the algorithm continuously estimates state-of-charge based on
adjusted net amp hours, battery capacity, initial state-of-charge, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which
is integrated to obtain net amp hours.
In addition, the electrical power management function is designed to perform regulated voltage control to
improve battery state-of-charge, battery life, and fuel economy. This is accomplished by using knowledge
of the battery state-of-charge and temperature to set the charging voltage to an optimum battery voltage
level for recharging without detriment to battery life.
The Charging System Description and Operation is divided into 3 sections. The first section describes
the charging system components and their integration into the electrical power management. The second
section describes charging system operation. The third section describes the instrument panel cluster
operation of the charge indicator, driver information center messages, and voltmeter operation.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > CHARGING SYSTEM COMPONENTS
Generator
The generator is a serviceable component. If there is a diagnosed failure of the generator it must be
replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces
an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of
diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the
vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator
integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator
controls the amount of current provided to the rotor. If the generator has field control circuit failure, the
generator defaults to an output voltage of 13.8 V.
Body Control Module (BCM)
The body control module (BCM) is a GMLAN device. It communicates with the engine control module
(ECM) and the instrument panel cluster for electrical power management (electrical power management)
operation. The BCM determines the output of the generator and sends the information to the ECM for
control of the generator turn on signal circuit. It monitors the generator field duty cycle signal circuit
information sent from the ECM for control of the generator. It monitors a battery current sensor, the
battery positive voltage circuit, and estimated battery temperature to determine battery state of charge.
The BCM performs idle boost.
Battery Current Sensor
The battery current sensor is a serviceable component that is connected to the negative battery cable at
the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor
monitors the battery current. It directly inputs to the BCM. It creates a 5 volt pulse width modulation
(PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent.
Between 0-5 percent and 95-100 percent are for diagnostic purposes.
Engine Control Module (ECM)
When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning
on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the
output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator.
When the engine is started, the regulator senses generator rotation by detecting AC voltage at the
stator through an internal wire. Once the engine is running, the regulator varies the field current by
controlling the pulse width. This regulates the generator output voltage for proper battery charging and
electrical system operation. The generator field duty terminal is connected internally to the voltage
regulator and externally to the ECM. When the voltage regulator detects a charging system problem, it
grounds this circuit to signal the ECM that a problem exists. The ECM monitors the generator field duty
cycle signal circuit, and receives control decisions based on information from the BCM.
Instrument Panel Cluster
The instrument panel cluster provides the customer notification in case a concern with the charging
system. There are 2 means of notification, a charge indicator and a driver information center message
of SERVICE BATTERY CHARGING SYSTEM if equipped.

[ctrlz]

DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > CHARGING SYSTEM OPERATION
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6
modes of operation and they include:
Battery Sulfation Mode
Charge Mode
Fuel Economy Mode
Head lamp Mode
Start Up Mode
Voltage Reduction Mode
The engine control module (ECM) controls the generator through the generator turn ON signal circuit.
The ECM monitors the generator performance though the generator field duty cycle signal circuit. The
signal is a pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal
duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic
purposes. The following table shows the commanded duty cycle and output voltage of the generator:
Commanded Duty Cycle Generator Output Voltage
10% 11 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 15.5 V
The generator provides a feedback signal of the generator voltage output through the generator field
duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The
signal is PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99
percent. Between 0-5 percent and 100 percent are for diagnostic purposes.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > BATTERY SULFATION MODE
The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 V for 45
minutes. When this condition exists the BCM will enter Charge Mode for 2-3 minutes. The BCM will then
determine which mode to enter depending on voltage requirements.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > CHARGE MODE
The BCM will enter Charge Mode when ever one of the following conditions are met.
The wipers are ON for more than 3 seconds.
GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control
head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the
BCM to enter the Charge Mode.
The estimated battery temperature is less than 0°C (32°F).
Battery State of Charge is less than 80 percent.
Vehicle speed is greater than 145 km/h (90 mph)
Current sensor fault exists.
System voltage was determined to be below 12.56 V
When any one of these conditions is met, the system will set targeted generator output voltage to a
charging voltage between 13.9-15.5 V, depending on the battery state of charge and estimated battery
temperature.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > FUEL ECONOMY MODE
The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F)
but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amperes and
greater than -8 amperes, and the battery state-of-charge is greater than or equal to 80 percent. Its
targeted generator output voltage is the open circuit voltage of the battery and can be between
12.5-13.1 V. The BCM will exit this mode and enter Charge Mode when any of the conditions described
above are present.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > HEAD LAMP MODE
The BCM will enter Head lamp Mode when ever the head lamps are ON (high or low beams). Voltage will
be regulated between 13.9-14.5 V.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > START UP MODE
When the engine is started the BCM sets a targeted generator output voltage of 14.5 V for 30 seconds.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > TOW/HAUL MODE
Pressing the Tow/Haul Mode button located on the center stack, the vehicle system voltage is raised
and the remote(non-vehicle) battery will be charged. Having the headlights on will raise the system
voltage and if the Tow/Haul button is applied it will not serve any purpose. The voltage is regulated
between 13.9-14.5 V.
DESCRIPTION AND OPERATION > CHARGING SYSTEM DESCRIPTION AND
OPERATION > INSTRUMENT PANEL CLUSTER OPERATION
Charge Indicator Operation
The instrument panel cluster illuminates the charge indicator and displays a warning message in the
driver information center if equipped, when the one or more of the following occurs:
The engine control module (ECM) detects that the generator output is less than 11 V or greater
than 16 V. The instrument panel cluster receives a GMLAN message from the ECM requesting
illumination.
The instrument panel cluster determines that the system voltage is less than 11 V or greater than
16 V for more than 30 seconds. The instrument panel cluster receives a GMLAN message from the
body control module (BCM) indicating there is a system voltage range concern.
The instrument panel cluster performs the displays test at the start of each ignition cycle. The
indicator illuminates for approximately 3 seconds.
Display Message: BATTERY NOT CHARGING SERVICE CHARGING SYSTEM or SERVICE BATTERY
CHARGING SYSTEM
The BCM and the ECM will send a serial data message to the driver information center for the BATTERY
NOT CHARGING SERVICE CHARGING SYSTEM or SERVICE BATTERY CHARGING SYSTEM
message to be displayed. It is commanded ON when a charging system DTC is a current DTC. The
message is turned OFF when the conditions for clearing the DTC have been met.

[avalonandl]

Yup we needed not one but TWO posts with mostly about nothing to do with the charging system which can very succinctly be stated as charging on demand.

Simply stated the system will charge when it needs to at about 12.1 volts and charges up to 14.2 volts.