Went to sea for 3 weeks , came back Vette was DEAD. So , I jump started it, took about 15 minutes (thinking battery here), then when it ran alternator, with Voltmeter, stated 14.4. Ran for about 15 minutes, drove it for 5, then shut it off, immediately restarted. Then backed it into the garage, tried to start it, nothing. I read the voltage on the battery, 12.4. Should be around 13.2? Anyways, do you think it is the battery or alternator?

 

Quick way to check is start the car and disconnect the neg battery cable ... if the car dies, it's the alternator; if not, it's the battery. (Sounds like it will be the battery based on what you said)

 

I would never do that.

You can never trust the in-car voltage gauge, always use an external gauge to check it. If the voltage is widely varying during normal operation, the regulator is bad and that will drain the battery eventually. If its reading above 13.5 during normal operation, and staying there roughly, then the alternator should be ok, and its likely the battery. If the car is shut off, the battery should be right around 12, but that doesnt mean its putting out the Amps to crank.

You may need to check out your fusible link, it can cause these symptoms as well.

 

Steve40th -- You've got mail from an old friend

 

Hi.
Just an recommendation.
I have an 85 and this might be the same for later models also.
I had batterydrain and could not understand it. I had the alternator checked and had a full overhaul. The same happened. Then I discovered that it wasthe courtesy light dimmer. This is a solid state module delaying the courtesy lights. It is placed taped on the cables on the passenger side under the dash just around the ECM. There has been much problems with this modul. To check it take the fuse out for the courtesy lights etc. On the 85 it is the upper left fuse. If it holds the charge then it is most probably the courtesy light delay "relay".
Charge the battery and next time you are away for some days even a week take out the fuse and see if the car starts again. It is a nasty problem. The dimmer might function "normally" with the delay on switching off the courtesy lights but even then can drain the battery.

 

I checked the battery with an external meter, FLuke. I also toook the battery out and checked it. I believe the alternator is working fine as the internal factory was steady and my fluke, at the alternator was good, no fluctuating.

 

The first mistake, when a battery is completely dead, you need a steady charge on it for at LEAST 8 hours at a 10 amp minimum to restore the life of the battery. A jump start is not enough to maintain a proper catalyst for the chemical reactions when you start it, your basically shorting the cells together which will seriously damage a cell, multiple cells, or the other charging system. The alternator does not have the proper charging capabilities to charge a from dead battery to "fully restored" battery. Also, this will put undue strain on the alternator diodes, they are not designed to handle a 100 amp inrush from a dead start. I'd recharge the battery properly and then look to see if there is a charging issue.

This happened to me two days ago when I left the interior light all night and it wiped my battery dry, followed my own advise and experience and 4 days later with no running, went out and the battery is 12.05V.......

Chris

 

I`ve got somewhat the same problem on my `87. Let it sit for a week, & the battery is dead. I`ve changed the alternator, & the battery. Let it sit for a week---- dead battery. Had it to the dealer, & they can`t find anything amiss. I`m going to do the same thing I did with the Harley. Getting a battery tender, & plugging it in every night. That way the battery will always be charged.

Ken

 

The battery was at 4 volts when I took it to SEARS, I think it was dying. Putting it in soon.
I do agree you need a slow charge to properly charge a battery, but after 5 years it may have been on its way. Before I left for sea, I was having problems with the alarm not letting me in. (Factory PKE). With 2 PKE's it wasnt responding. Then I slimmed it open, put the key in and it was alittle hard to start, but it started. SO , I think the battery is/was bad.
Thanks for the help guys, Steve

 

Kittmaster has it nailed. 10 amp battery chargers are inexpensive and handy to have around. It's one of those items you never need until you need it, like one of those cheap 12 volt tire pumps. I also have one of the 12 volt impact wrenches for removing wheel lug nuts in seconds; sweet! On the original subject, alternators used to "recharge" batteries have a remarkably short life span. They won't get it done and they'll fry themselves to death trying. (I think the Kittmaster already said that!)

 

Driving for 20 minutes will not charge your battery up very much and puts a large current load on the alternator which will shorten its life. Always recharge your battery with a battery charger. You can tell the state of charge by measuring the no load (and after sitting for 12 hours) battery terminal voltage. 12.0 volts and below, discharged. 12.9 volts and above, fully charged. The design center output voltage from your alternator is 14.7 volts cold and this will fall to 13.7 hot. Removing the negative terminal and placing an ammeter in series between the bat neg terminal and the cable will allow you to measure the leakage current after the courtesy lights time out. GM says the leakage current should not exceed 50 ma. My 87 measures 28 ma.
High leakage current will discharge your battery quickly. NEVER let your battery sit for long periods (4 wks) doing nothing, even disconnected. Lead acid batteries self discharge 1% each day and lead sulfate collects on the plates during discharge and lead sulfate is an insulator. Fully sulfated, a battery will not draw any current when attempting to recharge it and you have a door stop at that point. If you have a battery charger, buy an interval timer (turns your lights on each evening when you aren't home) and set it for its minimum interval (usually 15 minutes) to charge the battery each day and your battery will always be charged and have a normal service life.