Hi Everybody,

I hope i can get some feedback on an experience i just had with my '79 928 (manual/euro). I did not drive it for 3 weeks, but it was on a simple trickle charger. Car started right up, drove 5 miles, had to wait on a open bridge while iddling for 15 minutes then drove another 5 miles. Parked the car for 45 minutes. Tried to start but would not start (would turnover, but only half a turn, feels like not enought power in the battery). Then after putting it on jump cables and a battery frpm another car it just started normal). Disconnected the cables drove the 10 miles home without a problem. Tried to start the car again 5 minutes after parking, started, started it again after 45 minutes: starts fine.

Anybody an idea, i think the accu is about 4/5 years old. Any tricks to pinpoint it? I am about to by a new Battery but just to be sure...

 

You just need a new battery.

 

Have the battery check at Walmart if available. They test the battery well and will let you know its condition.

 

Hi Thanks for the feedback, i am located in the Netherlands so no wallmart here

 

+1 on Walmart having better battery test equipment. I learned that the hard way.

You can check the alternator output with a multimeter using either the battery terminals (with the car running of course) or use the front jump post, positive lead there and negative to a bolt on the engine. If good the battery is shot.

 

I guess I should just add this, because it happened to me. They could actually both be bad or heading in that direction. You’ll find out for certain after you replace one, but I hope that’s not the case for you.

 

Always start checking at the beginning of the power source.........battery.

 

In the US most auto parts stores have a battery load tester.

Your country probably has some as well in your parts store equivalents. If not, I'm sure any of the local garages will be happy to test your battery for you.

 

Just been through this, very similar symptoms to OP. Suspected both battery and alternator. Charged it to full, then went OS, left it sitting uncharged, isolated for 5 weeks - started fine, battery is OK, despite being nearly 5 years old. Started up in driveway, watched volts. 14.2, 14.1 for around 15-20 minutes, then it dropped to 12.3, 12.2, 12.1 - alternator failing when hot. Went to recommended sparky, expecting to have to get mine refurbed, but he had a brand new unit complete with long through bolts on the shelf!
jp 83 Euro S AT 57k

 

It's not as scientific, but simple checks with a voltmeter can tell A LOT about the health of a battery.

You want to see between 12.3V ~ 12.8V on a battery that has been at rest for at least 12 hours. A good battery can of course fall out of this range. Charge the battery. Sometimes these batteries will need to sit on a charger for 48-72; hours, so be patient. Connect your voltmeter to the battery immediately after charging. If the battery is at less than 9V, then it is toast! If it's 10V or more, then it needs to rest and be checked again in a couple of hours. If the battery stabilizes at anything north of 9V, it might be worth it to try charging again.

 

i went for the most obvious en easy solution and i just replaced the battery. No more problems (will report bak when it does not fix it)...thx everybody!

 

I use this real time monitor to check while I drive
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I run one of these on a couple of cars (those with oldest batteries). Strange large fluctuations on the cranking display, and a charging voltage under 14v would worry me. All my cars start off showing 14.7V straight after startup, tapering down to 14.1-14.3V after the cranking drain has been replenished. Same volts show on modern cars with ODB-II. In fact when I had the recent alternator failure, after start I got 14.1V for 15mins, then it failed to produce any output at all once hot.

jp 83 Euro S AT 57k

 

Thx for the reply! Looks like an app? What is it exactly?

 

https://www.ebay.com/itm/Battery-Mon....c100290.m3507