As soon as the weather gets cold the volt gadge goes upto about 3/4. Do I need a new battery or is the alternator over charging the battery

 

You know its funny you post this, I just noticed my truck does the same exact thing. I think my battery is about 3 yrs. old, my guess is the batt. is not 100% anymore and the cold is taking its toll on it. I guess well just wait and see. Actually yesterday, I started my truck first thing in the AM and the temp. gauge shot up to max and the check gauges light came on. Checked all wiring, sender etc. and all looked fine. Restarted the truck and it was fine. I dunno maybe the cold temps have been screwy with the truck ha

 

Throw a DMM on your battery and see what it's charging at. Dash gauges while a nice ballpark never seem to be overly accurate.

 

I would usually pick on the voltage regulator right away, but the ECU in these trucks controls the voltage to the battery; therefore i would say you battery might have bad cells. You can take it out and have it checked out by your locak parts store. They can load test and charge check it for free.

First off, check your connections to verify their correctness and that the terminals are clean and not goobered all up with acid residue. Also, if you have a multimeter, you can idle your truck with all accessories and lights off and read the voltage across the battery to verify your dash guage is reading correct.
I know the computer monitors battery temp, engine speed and all that to charge sufficiently, so maybe there's something wrong elsewhere? Verify the obvious first and go from there.
post back with your results.

 

What DD said and be aware that there is a temperature sensor under the battery that provides input to the PCM to help regulate the charge.

 

^^^ Exactly, remember that battery temp sensor is under there and it a resistance type sensor. As said above, the PCM regulates the voltage based off of the readings that $50 sensor gives. Every winter we see guys come in and say the same thing. IMO, you are normal. But if you have an older battery you should check the acid level in it and make sure it is full so you can produce and keep a good charge at all times.

 

A battery temperature sensor, located in the battery tray housing, is used to sense battery temperature. This temperature data, along with data from monitored line voltage, is used by the PCM (ECM Diesel) to vary the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly

OPERATION

The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM (ECM Diesel) to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures. The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases. The BTS is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled, depending upon BTS input (for example, disable purge and enable Leak Detection Pump (LDP) and O2 sensor heater tests). Most OBD II monitors are disabled below 20°F.

 

my pcm no longer regulates the charge. boo that crap. i let the alt do its job (and its been doing that for 3years now).
i ran 0gauge straight from the alt to the battery, THEN to the fuse box. i wouldn't recommend this for a normal stock setup though... i am running 6000watts rms, and a 1200cca batt, and have heavily modified my wiring to suit.

 

I haven't looked this up recently, but I believe the PCM regulates the field voltage of the alternater. So connecting a wire from the alternater output to the battery doesn't change anything other than maybe upgrading it's current carrying capability. Now if you have jumped the alternater's field winding, that might be another story. interesting idea.... I bet you could burn up stuff you have never dreamed of.

 

hahahaha.. yes...yes you can. i was running a 400amp 16volt alt in my blazer and the regulator went out..... needless to say. that was a wiring NIGHTMARE