New dead battery

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Charles Ricciardi
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New dead battery

#1 Post by Charles Ricciardi »

Awaking to the first nice day since November, I was happy to take my 1958 cabriolet out of the garage for a short trip to the store. So I disconnected my trickle charger, and it fired right up and off I went. Ten minutes to the store, ten minutes in the store and when I came out, a dead battery. Replaced the battery with a new one. Kept it on the charger until I took the car out on the next nice day. Drove great and put it away for the evening without re-hooking the charger. Tried to start it the following day and the new battery was dead. Jump started it and drove it 60 miles to the beach hoping to recharge the battery on the trip. Got to my destination, turned the car off and tried to restart...dead battery. So after charging the battery it starts great, but after driving, as short a time as 45 minutes, the battery is dead . At first I though I had a parasitic electrical short that was draining my battery overnight but now it doesn't seem to charge while driving, but it will run for 90 minutes, and then present me with a dead battery. What up?

Michael Pawelek
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Re: New dead battery

#2 Post by Michael Pawelek »

I would wonder if the generator in the 356 is charging the battery properly.

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Martin Benade
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Re: New dead battery

#3 Post by Martin Benade »

I’d expect it to do better than this just running on the battery. I wonder if the generator is somehow drawing current instead of charging.
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Mike Wilson
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Re: New dead battery

#4 Post by Mike Wilson »

I'd check both the generator and voltage regulator.

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David Jones
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Re: New dead battery

#5 Post by David Jones »

Should not take long to diagnose even without a voltmeter. Adjust the RPM's up until the generator light goes out then disconnect the battery. If the engine keeps running then the generator is charging. To check with a voltmeter raise the RPM to about 2500 then check charging voltage. Should be somewhere near 7.3 volts.
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Geoff Fleming
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Re: New dead battery

#6 Post by Geoff Fleming »

The exact scenario happened to me a few decades ago with my factory 12volt coupe.
It turned out to be a faulty regulator , which was not allowing the battery to re-charge.
As in your case, I instinctively replaced the battery, only to experience the same symptoms.
Follow David’s advice to eliminate the generator as a culprit.

Charles Ricciardi
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Re: New dead battery

#7 Post by Charles Ricciardi »

Thanks for the input. Went and bought a voltmeter. The battery is not dead. trickle charger seems to be working. Battery shows 6.4 volts. When I turn the key clockwise in the pre ignition position, the generator and oil pressure light came on and the radio worked. Then upon turning the key to ignition, all goes dead in the car. The battery still shows a charge. Waited 20 minutes and turned the key to pre ignition and my warning lights came on again. I tested the fuse connectors at that time and the 4 fuse connectors on the right hand side of the fuse box registered 6.4 volts. Tried to start again. Something in the engine compartment tried to jump to life, but the car went dead again. The 4 fuses now only test at 1.4 volts.

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David Jones
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Re: New dead battery

#8 Post by David Jones »

Go to the battery and at the battery positive connection there's a fairly thick red wire as well as the heavy oneto the starter. It may be loose or corroded. Clean and secure it, it may well solve your problem.
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Martin Benade
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Re: New dead battery

#9 Post by Martin Benade »

And clean the main + and - terminals too.
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Jules Dielen
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Re: New dead battery

#10 Post by Jules Dielen »

And check if you have + to + and ground to -. My neighbor somehow made that happen, even though they are different sized posts. His Volvo did all kinds of weird things and would not crank.
Last edited by Jules Dielen on Tue May 28, 2024 12:26 am, edited 1 time in total.
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Charles Ricciardi
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Re: New dead battery

#11 Post by Charles Ricciardi »

I'll give that a try and let you know the outcome. Wont see the car till Friday

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Re: New dead battery

#12 Post by Hugo Karasawa »

Check if both batteries can hold the charge, even if you have a new one it can be damaged, the stores where they sell the batteries can check those for you.
If the batteries are fine, check for a parasitic current draw, if it is too high you have a problem there.
Lastly, check your charging system, read Greg Bryan´s articles. Registry Magazine march/April 2016 and July/august 2016.

Or buy an unexpensive battery analyzer to do these test. This one has worked for me.
Kingbolen Battery analyzer.jpg

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