: 1979 CDV battery going dead in under an hour.

04-11-11, 07:11 PM
Denice (the red '79) is having a problem. There's some kind of major battery drain. You can literally charge the battery, drive it around, wait less than an hour, try to start it again, and the battery will be dead. It's been getting worse over the last year or so. You see, the car isn't with me right now. It's at my parent's house. My Dad has taken a shining to Denice & has been taking care of her since I moved to Chattanooga.

This is exactly what he has to say about the problem

1979 Cadillac DeVille Coupe

An Everstart 12-volt 75-5N battery was installed on 7/21/2009. At first, the vehicle started easily with minimal cranking. In a short time, the battery was lifeless and had to be recharged. Suspecting a drain on the battery, the negative ground cable was detached between engine startups. This seemed to solve the problem for a short time, however when the negative cable was reconnected, the
Vehicle still would not start without a charge. The owner checked the battery to make sure the battery had water and the cells were full. The Alternator light is working and does not come on when the engine is running.

Even with disconnecting the negative cable between starting, the battery still appeared dead. After recharging the battery using a Sears brand charger, the charger indicated the battery was 100% charged. However when attempting to start the engine, all it did was “click.” It appeared the battery still was totally dead. The owner then set the charger for 125A immediate start, and then the vehicle would start.

The situation deteriorated to the point where the vehicle failed to crank even with the 125A “super charge.” The owner finally jump started the vehicle using jumper cables from his 1999 Nissan Sentra battery—also an Everstart battery. At last the vehicle started.

The own suspects this battery simply is too underpowered for this vehicle, and welcomes any advice from the reader.

And ideas are very welcome. I know he has a volt meter, but I'm not sure what to do with it. I guess I just want to know what the most likely causes would be, and what else we can do to diagnose the problem. He's trying to get Denice back on the road as a second car, and this is a pretty big hitch in the master plan.



04-11-11, 08:53 PM
First step is to get the battery tested. It may not be able to hold a charge. Then, get the alternator tested.

If the battery and the alternator are good, disconnect the positive terminal and put an ammeter in series with the battery and the lead. Note the current draw. One by one, checking the ammeter each time, start pulling fuses. You have found your problem when the amps drop.

My money is on a bad battery or alternator, with second place answer: stuck relay.

04-11-11, 09:01 PM
A 75 series battery is correct for that car, so the battery is not inadequate.

A functioning CHARGE light does not actually mean that the alternator is working. Have him have the alternator tested. It takes 11 volts to make the engine crank; any less and you will barely get the starter to click. The ignition coils can run on less than 10 volts, so running the engine with a malfunctioning alternator will drain the battery beyond the minimal crank voltage.

Disconnecting the negative rules out any parasitic drain. Have him take his DVOM and confirm that the battery is holding about 12.5 volts. If the engine still wont start, then have him replace the positive cable to the starter. High resistance in the starter cable will mimic the symptoms of a dead battery, and unless the battery is as charged as it can get, it will not turn the starter.

04-12-11, 04:04 AM
I'm betting alternator also...and battery has become a victim of the alt.

04-12-11, 08:44 AM
I agree with the above statements. Something similar happened to my crown vic (though in the opposite) the battery got a hole in it and wouldn't hold a charge and caused the alternator to die...but the charge light never came on (although it did work)

get the battery and alt checked.

04-12-11, 08:48 AM
Also check the battery and starter grounds. The ground from the negative post to frame has a tendency to oxidize and cause similar problems.

04-13-11, 10:13 PM
The Battery in my phaeton is acting up, if I leave a door open for 10 mi while detailing it barely starts, yet I had it tested and it gave decent results so I will swap it out soon for a correct AC delco