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Battery Draining While Driving - SOLVED
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davidw99
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PostPosted: Mon Sep 26, 2016 4:56 pm    Post subject: Battery Draining While Driving - SOLVED Reply with quote

I know similar topics have been covered here (and I've read most of them) but I still can't figure out what's going on with my car.

The car will start and drive beautifully but after a period of days to weeks, the car starts more and more slowly until the battery is dead. The battery will hold a charge when charged with a trickle charger. Did this today and after the charge the reading was 13.02 volts. I started the car and the alternator was putting our 14.31 volts. With lights on - 13.81 volts.

With the key on I had 12.55 volts at the ignition wire at the coil and 12.21 volts at the alt wire to the D+ term on the alternator.

Yesterday I was driving for about 45 minutes at highway speed and stopped to get a cup of coffee. The car wouldn't start when I got back to it. All the symptoms of a drained battery. The car had been starting more and more slowly up till this point. I called AAA for a jump. The car drained the battery jump box in about 10 seconds and the car did not start. The AAA guy seemed very surprised by this but did not have any insights. I had to have the car towed. When I got home I tested the battery and it read well under 12 volts (can't remember the actual number) and went below 9 volts when I tried to start the car. I put the trickle charger on and got the readings I posted above after charging. The car started right up. This problem has been on going.

Other things I've done recently trying to solve this problem: cleaned trans ground strap at both ends, cleaned battery cables and ground and starter connections. The battery is new this year. The old battery (two years old) had the same symptoms. One cell in the battery was slight low on water. It could have come that way. The alternator is new this year (and working well by the numbers above). The electrical part of the ignition switch is new this year.

So, for some reason, the battery does not seem to be charging from the alternator and/or holding a charge. Battery will charge with trickle charger and alternator seems to be functioning. I'm stymied. Any thoughts? Any and all help appreciated.
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Last edited by davidw99 on Sun Oct 02, 2016 5:45 am; edited 1 time in total
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Cusser
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PostPosted: Mon Sep 26, 2016 6:32 pm    Post subject: Re: Battery Draining While Driving Reply with quote

I suspect the alternator.
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Multi69s
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PostPosted: Mon Sep 26, 2016 9:35 pm    Post subject: Re: Battery Draining While Driving Reply with quote

Take your meter with you on your next drive. Then before you shut off the engine, measure the output voltage of the alt, and take a reading at the battery posts. If there is a difference, it is probably a cable that is internally corroded.
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davidw99
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PostPosted: Tue Sep 27, 2016 2:43 am    Post subject: Re: Battery Draining While Driving Reply with quote

I'll give that a try. Do you mean a cable from the alt or in the alt?
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davidw99
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PostPosted: Tue Sep 27, 2016 6:35 am    Post subject: Re: Battery Draining While Driving Reply with quote

Multi69s, I just reread you posting. How do I "measure the output voltage of the alt"?
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PostPosted: Tue Sep 27, 2016 6:54 am    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
Multi69s, I just reread you posting. How do I "measure the output voltage of the alt"?


I believe it would be positive lead of meter to B+ terminal on alternator and negative lead of meter to any good ground. It should read the same as the battery reading.
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PostPosted: Tue Sep 27, 2016 7:01 am    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
Multi69s, I just reread you posting. How do I "measure the output voltage of the alt"?


I believe it would be positive lead of meter to B+ terminal on alternator and negative lead of meter to any good ground. It should read the same as the battery reading.
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davidw99
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PostPosted: Tue Sep 27, 2016 7:37 am    Post subject: Re: Battery Draining While Driving Reply with quote

Thanks.
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PostPosted: Tue Sep 27, 2016 7:42 am    Post subject: Re: Battery Draining While Driving Reply with quote

If you are getting 14V out of the alternator while running but your battery is still dying/not holding a charge then I would suspect the battery itself is bad. How old is it?
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PostPosted: Tue Sep 27, 2016 8:01 am    Post subject: Re: Battery Draining While Driving Reply with quote

Cusser wrote:
I suspect the alternator.


Disconnect the negative battery cable when not driving for a few days; this will help isolate if battery itself is holding a charge, or if the battery is discharging overnight/over few days.

I have read about alternators that charge fine with engine running but discharge/drain while sitting.
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PostPosted: Tue Sep 27, 2016 8:29 am    Post subject: Re: Battery Draining While Driving Reply with quote

sjbartnik wrote:
If you are getting 14V out of the alternator while running but your battery is still dying/not holding a charge then I would suspect the battery itself is bad. How old is it?


Just a couple of months.
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davidw99
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PostPosted: Tue Sep 27, 2016 8:32 am    Post subject: Re: Battery Draining While Driving Reply with quote

Cusser wrote:
Cusser wrote:
I suspect the alternator.


Disconnect the negative battery cable when not driving for a few days; this will help isolate if battery itself is holding a charge, or if the battery is discharging overnight/over few days.

I have read about alternators that charge fine with engine running but discharge/drain while sitting.


But wouldn't the battery recharge while driving? How long would it take for the alternator to recharge a battery?
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PostPosted: Tue Sep 27, 2016 8:46 am    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
Cusser wrote:
Cusser wrote:
I suspect the alternator.


Disconnect the negative battery cable when not driving for a few days; this will help isolate if battery itself is holding a charge, or if the battery is discharging overnight/over few days.

I have read about alternators that charge fine with engine running but discharge/drain while sitting.


But wouldn't the battery recharge while driving? How long would it take for the alternator to recharge a battery?


If a battery has been drained to the point where it needs to continually be recharged, then it has a dead cell and will no longer hold a constant charge no matter how long or how many times you recharge it. It might recharge enough to start the car initially, but it won't hold that charge.
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PostPosted: Tue Sep 27, 2016 8:49 am    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
Cusser wrote:
Cusser wrote:
I suspect the alternator.


Disconnect the negative battery cable when not driving for a few days; this will help isolate if battery itself is holding a charge, or if the battery is discharging overnight/over few days.

I have read about alternators that charge fine with engine running but discharge/drain while sitting.


But wouldn't the battery recharge while driving? How long would it take for the alternator to recharge a battery?


If a battery has been drained to the point where it needs to continually be recharged, then it has a dead cell and will no longer hold a constant charge no matter how long or how many times you recharge it. It might recharge enough to start the car initially, but it won't hold that charge.
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PostPosted: Tue Sep 27, 2016 8:50 am    Post subject: Re: Battery Draining While Driving Reply with quote

When charging the battery both the alternator and a stand-alone battery will charge at a voltage higher than (13.8-15.0v) the normal battery voltage (12.6v). If you measure the battery voltage as soon as you take the battery off the charger you will get a surface charge reading. Like you did earlier (13.02v). This voltage reading alone will not tell you if the battery is fully charged.
Install the battery in the car and crank the engine once or twice. You might even want to disconnect the ignition coil for this test. You are not trying to start the engine, you are just trying to draw off the surface charge from the battery to get a true reading of its state of charge. Once you've done this, turn everything OFF and take a measurement at the battery posts. A fully charged battery in good shape should still read 12.6v. If you get a voltage reading lower than this then your battery was not fully charged (put back on the trickle charger) or it is old and can no longer hold a full charge.
The above is similar to a load test that your FLAPS or local shop could run on your battery. A load test is a much better measure of the quality of your battery than just a voltage test.
FYI, 12.2v is 50% state of charge (SOC) and 11.5v is 0% SOC. Don't think that a battery reading 11.0v is "good enough". A battery below 12.0v is already too weak to properly run solid state devices (eg. electronic ignition modules and radios) that require 12.0v to operate properly.

I suspect your battery, but more testing is needed to confirm.

Testing your alternator should be done at the battery terminals. You might get a false sense of having a good charging system if you get 14.0v at the B+ terminal of the alternator when in fact only 13.5v is making it to the battery posts. You want a min of 13.8v at the battery with the idle up around 2000rpms.
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PostPosted: Tue Sep 27, 2016 9:32 am    Post subject: Re: Battery Draining While Driving Reply with quote

Thanks. I'll check it when I get home tonight. I've started the car once, had a short drive and it will have been sitting for about 24 hours. I'll try the starting with the coil wire unplugged also.
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PostPosted: Tue Sep 27, 2016 3:00 pm    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
I've started the car once, had a short drive and it will have been sitting for about 24 hours.

That should have taken any surface charge off the battery. Take a reading at the battery posts before you turn anything ON. Sitting for a day or so after charging should also allow the battery voltage to drop to normal levels.

Just note, the test of taking a voltage reading while the engine is running to check the charging system is dependent on having a fully charged battery installed. If your battery is outputting 12.6v and your alternator is outputting 14.5v the reading you get at the battery posts with the engine running may be around 13.8v. But if your battery is weak and only has a 12.0v charge, when tested with the 14.5v alternator output may only read 13.0v making you think the charging system is bad. You need a fully charged battery (12.6v) before you can test the alternator output voltage. Anything less and it will impact your readings.
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PostPosted: Tue Sep 27, 2016 3:26 pm    Post subject: Re: Battery Draining While Driving Reply with quote

OK. I took a reading at the battery and got 12.56. I turned the car over with the coil wire off and got 12.44 afterwards, However, the car turned over very slowly almost to the point of not turning over after about 20 seconds. A specific gravity tester showed fair, which I'm guessing is consistent with a 12.44 volt reading.

Could the problem be the starter and it needs a full battery charge to get going? Maybe this explains why the AAA man's battery box didn't work? If it is the starter it has been failing for a while. The only other time I had a starter go it just stopped working. Thoughts?
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PostPosted: Tue Sep 27, 2016 5:04 pm    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
OK. I took a reading at the battery and got 12.56.

That is fine.

davidw99 wrote:
I turned the car over with the coil wire off and got 12.44 afterwards, However, the car turned over very slowly almost to the point of not turning over after about 20 seconds. A specific gravity tester showed fair, which I'm guessing is consistent with a 12.44 volt reading.

This is not a good sign. Either your battery was NOT fully charged, or it was and is in bad shape such that it cannot hold a charge. One or two starts should not cause a two month old battery to drop so much that the starter has a hard time turning.
Take a known good battery from another car and jump start your car. If having the extra battery connected allows the starter to easily crank the engine then it indicates your battery was weak. Again, cannot tell at this point if it was not yet fully charged or just bad. It wouldn't hurt to get it fully charged (trickle charge overnight) and take it to your FLAPS and have them load test it. As long as the battery is fully charged, they should be able to tell you if the battery is bad or not.


davidw99 wrote:
Could the problem be the starter and it needs a full battery charge to get going? Maybe this explains why the AAA man's battery box didn't work? If it is the starter it has been failing for a while.

This is akin to saying... "The 9v battery in my radio is only at 8v. Maybe it only works when the battery is at 9v. I wonder if my radio needs to be replaced?"
If you have a known good battery that you can temporarily put in place of the questionable one and see if it immediately starts the engine. This would point to your battery being bad or not fully charged.

FYI... deep discharging a lead-acid battery will sulfate the plates and render them less efficient. Do this too many times or one REALLY deep discharge and your battery may no longer hold enough of a charge to crank the engine.
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PostPosted: Tue Sep 27, 2016 6:46 pm    Post subject: Re: Battery Draining While Driving Reply with quote

davidw99 wrote:
However, the car turned over very slowly almost to the point of not turning over after about 20 seconds.


THAT'S the voltage reading across the battery terminals that we need, like 10 to 20 seconds into cranking or trying to crank !!! That's voltage under load, post that. Hint: should be over 9.6 volts with good battery.
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