Dead or Dying Battery, or?

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DartGTDan

DartGTDan

'71 Dart GT Fan
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Saturday I was out driving my car ('71 Dart GT 318) around town at speeds up to 50 mph. As the vehicle speed increased I noticed the voltage would also increase to just over 16V (which I do not recall seeing it ever go that high before). When I would come to a stop, with the transmission in Drive, the voltage would drop down to ~12V. During this trip I was not using anything electrical (wipers, headlamps, blower fan, etc...).

Sunday, my wife and I took a drive to the cemetery (the 5th anniversary of her dad's passing), then to a local ice cream parlor. During this trip the voltage appeared to be normal (~12V at a stop and ~14V while at speed).

This morning I drove it to work (as I had an appointment to drop it off at the body shop directly after work) with the headlamps on. Again, the voltage appeared to be functioning normally (~12V while stopped and ~14V at speed).

After work, the volt gauge was reading just a hair under 10V no matter what speed I was traveling. Fortunately, I made it to the body shop without incident.

Unfortunately, I cannot remember when I purchased the battery, but I'm sure it has to be at least 5 years old. The last time the battery died, it was a "sudden death" (as in, I shut the car off, and it would not re-start 5 minutes later). I've never experienced a "dying battery".

Am I correct in assuming the battery is dying? Or?
 
DartGTDan said:
Saturday I was out driving my car ('71 Dart GT 318) around town at speeds up to 50 mph. As the vehicle speed increased I noticed the voltage would also increase to just over 16V (which I do not recall seeing it ever go that high before). When I would come to a stop, with the transmission in Drive, the voltage would drop down to ~12V. During this trip I was not using anything electrical (wipers, headlamps, blower fan, etc...).

Sunday, my wife and I took a drive to the cemetery (the 5th anniversary of her dad's passing), then to a local ice cream parlor. During this trip the voltage appeared to be normal (~12V at a stop and ~14V while at speed).

This morning I drove it to work (as I had an appointment to drop it off at the body shop directly after work) with the headlamps on. Again, the voltage appeared to be functioning normally (~12V while stopped and ~14V at speed).

After work, the volt gauge was reading just a hair under 10V no matter what speed I was traveling. Fortunately, I made it to the body shop without incident.

Unfortunately, I cannot remember when I purchased the battery, but I'm sure it has to be at least 5 years old. The last time the battery died, it was a "sudden death" (as in, I shut the car off, and it would not re-start 5 minutes later). I've never experienced a "dying battery".

Am I correct in assuming the battery is dying? Or?
Click to expand...

It could be the battery, but from the description of the symptoms I would check all the connections first.
Alternator, battery cables and even at the regulator plug.
 
I would check the voltage to the field ( from the voltage regulator) while it is not charging well.
 
THIS IS WHY (guys and girls) "we" need to learn to troubleshoot, unless "you like" throwing money at it

Possibilities..........green field connection or that end of rotor is grounded causing "full field" charging
VR is UNgrounded
VR is actually defective
Harness voltage drop---the "usual" problem
I dont see a bad battery causing those symptoms, but a bad battery can cause things like never returning the ammeter to zero

Start car run at fast idle, monitor battery voltage. Disconnect VR. If voltage drops to below 13, alternator rotor/ field/ brushes are not shorted

Remove VR scrape mounting bolts and remount making certain it is grounded

If voltage is still high, check for voltage drop in harness

If voltage drop tests are OK replace VR

To check for voltage drop, turn key to run, engine stopped. Hook one end of meter to "key" side of ballast, stab the other into the battery POS post. You are hoping for a reading below .3V (3/10 of one volt) If reading is a volt or more this explains the over-charge

To check "ground" side, run engine at fast idle, make the following check first with accessories off, and again with lights, heater, etc running

Stab one probe into battery NEG post and stab other into VR mounting flange, make sure to stab through paint, rust, etc. Once again, the lower the reading the better, zero is perfect.

The voltage drops measured above will result in the addition of charge voltage, that is IF the VR is correctly working at about 14V and you have 2V drop in the above measurements, the system will charge at 16V
 
67Dart273 is spot on. I've followed his advice over the years, and always found the culprit without "easter egging." Do you still have the original VR? I'd start there after making sure ALL grounds are correct. If you have a buddy with an O'Scope, that can be an immense help, as you can see things that won't show up with just a DVM. Please keep us advised.
 
As stated, could be a variety of fixes. Diagnostics, diagnostics, diagnostics. DO NOT rely on your local fix it shop to find the problem, most do not understand non computer cars.
 
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