Voltage Fluctuation on 2006 Dodge Ram 2500

On my 2006 Dodge Ram 2500 Diesel sometimes after starting voltage indicator will discharge with lights dimming, then will move back up to charge with lights becoming brighter. This occurs mostly in cold weather.It will do this sometimes up to 15 minutes after starting, Discharging then charging, discharging then charging.

Asked by for the 2006 Dodge Ram 2500
In Cold weather it is quite normal for the Volt meter to go below 12 volts and dim the lights. Assuming your battery or batteries are in good condition, this is because of the fuel heaters which turn on in cold temps. These heaters draw a considerable amount of current during the first few minutes of running. The fuel heater is used to prevent diesel fuel from waxing during cold weather operation.

When the fuel temperature is below 45° ±8 F (7°C), the temperature sensor allows current to flow to the heater element warming the fuel. When the fuel temperature is above 75° ±8 F (24°C), the sensor stops current flow to the heater element.

Battery voltage to operate the fuel heater element is supplied from the ignition switch and through a solid stated device in the IPM. The fuel heater element and "solid state device in IPM" instead of "fuel heater relay" are not computer controlled. The heater element operates on 12 volts, 300 watts at 0° F (-18° C).
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alternator has a problem internally. get it verified and you will probably need a replacement.