Battery stays a bit low--bad or normal?
10-10-2016, 05:37 AM
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Battery stays a bit low--bad or normal?
Chasing some other things, I noticed that my battery voltage was a bit low, though the car starts OK. Disconnected it from the car and put it on a old-style (not "smart") charger that was about 14.1 volts. After a few hours, pulled it off and it was 12.77V, decaying to 12.59 after 45 min. About 6 hrs later it was 12.52V and about 10 hours after that it read 12.48V. This is all in the garage, so there's not much temperature change. Tried charging again (not for long), 25 minutes after charge it was 12.60 V.
At that point I took it to Adv Auto and they read 12.55V and 740 CCA vs a spec of 790, so it passes. Now, about 22 hours later, I get 12.45V (on my meter). The battery's 2 years old. I have seen a few shifts in the voltmeter reading on the dash while driving, but it's hard to tell for sure. Cleaned the terminals, ground strap, and strap from engine block to chassis; couldn't easily get at the positive lines but everything else was just fine. I had about 14 V at the battery terminals when idling the car. When I reinstalled the battery, the current draw was about 170 mA (on a 10 A scale, to deal with the initial inrush) but might have still been declining slowly. Seems a little high--normal for this car?
I've seen the voltage as low as 12.08V over the days of monitoring this. Alternator is about 7 years old on a rebuilt, and that was not a happy event, so maybe I'm twitchy about this. Chasing a ghost or all normal? Why won't the battery go about 12.6V and why does it lose ~0.1 V overnight? If it is the battery, how do I convince Advanced of that?
Thanks!
At that point I took it to Adv Auto and they read 12.55V and 740 CCA vs a spec of 790, so it passes. Now, about 22 hours later, I get 12.45V (on my meter). The battery's 2 years old. I have seen a few shifts in the voltmeter reading on the dash while driving, but it's hard to tell for sure. Cleaned the terminals, ground strap, and strap from engine block to chassis; couldn't easily get at the positive lines but everything else was just fine. I had about 14 V at the battery terminals when idling the car. When I reinstalled the battery, the current draw was about 170 mA (on a 10 A scale, to deal with the initial inrush) but might have still been declining slowly. Seems a little high--normal for this car?
I've seen the voltage as low as 12.08V over the days of monitoring this. Alternator is about 7 years old on a rebuilt, and that was not a happy event, so maybe I'm twitchy about this. Chasing a ghost or all normal? Why won't the battery go about 12.6V and why does it lose ~0.1 V overnight? If it is the battery, how do I convince Advanced of that?
Thanks!
10-16-2016, 10:30 AM
#3
AudiWorld Super User
Since you've spent so much time, how about spending some money on a load tester?
Chasing some other things, I noticed that my battery voltage was a bit low, though the car starts OK. Disconnected it from the car and put it on a old-style (not "smart") charger that was about 14.1 volts. After a few hours, pulled it off and it was 12.77V, decaying to 12.59 after 45 min. About 6 hrs later it was 12.52V and about 10 hours after that it read 12.48V. This is all in the garage, so there's not much temperature change. Tried charging again (not for long), 25 minutes after charge it was 12.60 V.
At that point I took it to Adv Auto and they read 12.55V and 740 CCA vs a spec of 790, so it passes. Now, about 22 hours later, I get 12.45V (on my meter). The battery's 2 years old. I have seen a few shifts in the voltmeter reading on the dash while driving, but it's hard to tell for sure. Cleaned the terminals, ground strap, and strap from engine block to chassis; couldn't easily get at the positive lines but everything else was just fine. I had about 14 V at the battery terminals when idling the car. When I reinstalled the battery, the current draw was about 170 mA (on a 10 A scale, to deal with the initial inrush) but might have still been declining slowly. Seems a little high--normal for this car?
I've seen the voltage as low as 12.08V over the days of monitoring this. Alternator is about 7 years old on a rebuilt, and that was not a happy event, so maybe I'm twitchy about this. Chasing a ghost or all normal? Why won't the battery go about 12.6V and why does it lose ~0.1 V overnight? If it is the battery, how do I convince Advanced of that?
Thanks!
At that point I took it to Adv Auto and they read 12.55V and 740 CCA vs a spec of 790, so it passes. Now, about 22 hours later, I get 12.45V (on my meter). The battery's 2 years old. I have seen a few shifts in the voltmeter reading on the dash while driving, but it's hard to tell for sure. Cleaned the terminals, ground strap, and strap from engine block to chassis; couldn't easily get at the positive lines but everything else was just fine. I had about 14 V at the battery terminals when idling the car. When I reinstalled the battery, the current draw was about 170 mA (on a 10 A scale, to deal with the initial inrush) but might have still been declining slowly. Seems a little high--normal for this car?
I've seen the voltage as low as 12.08V over the days of monitoring this. Alternator is about 7 years old on a rebuilt, and that was not a happy event, so maybe I'm twitchy about this. Chasing a ghost or all normal? Why won't the battery go about 12.6V and why does it lose ~0.1 V overnight? If it is the battery, how do I convince Advanced of that?
Thanks!
Get your own load tester, use it once or twice a year.
10-17-2016, 07:06 PM
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A little update. Had a long drive Friday, much at highway speed, and upon return the battery was about 12.55 V. Faded to 12.4 -ish overnight. I did have fairly high current drain, nearly 200 mA, but still--that's only a couple amp-hours on a big battery. (Pulling the iPod out and the radio fuse gets that under 100 mA; the radio is 60 mA by itself.)
I load tested the alternator over the weekend using the headlights, radio, seat heater, defroster and blower. Dropped from ~14.1 to maybe 13.8 or 13.85 with all that. Steady (
I load tested the alternator over the weekend using the headlights, radio, seat heater, defroster and blower. Dropped from ~14.1 to maybe 13.8 or 13.85 with all that. Steady (
10-18-2016, 07:53 AM
#6
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A brand new battery sitting on the shelf at the auto parts store will read about 13.2 volts if you check it with a meter ( that's at around 65F to 70F degrees ambient temperature). Without being there to personally check this, I would say your alternator isn't putting out as it should. Especially after long drive at highway rpm. If you can remove the alternator easily, do that and take it to a parts store that can bench test it. If you have a bad battery that can over-work the alternator and in turn make it fail.
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10-18-2016, 03:13 PM
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Yes! No easy removal--you have to assume the "service position". OK, I know it can be done in an hour (some claim 15 min) but it's certainly a PITA/no-fun job, including draining and refilling coolant.
I might have caught it in the act tonight. Driving home from work the meter was low of the 14V mark--read 13.78 V in my driveway, warm, at idle, lights and radio off. Might be an intermittent. I'm borrowing a scope to look at the waveform--I'm thinking blown diode in the alternator.
I might have caught it in the act tonight. Driving home from work the meter was low of the 14V mark--read 13.78 V in my driveway, warm, at idle, lights and radio off. Might be an intermittent. I'm borrowing a scope to look at the waveform--I'm thinking blown diode in the alternator.
10-18-2016, 05:49 PM
#9
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I'm thinking you will need to do the service position anyway cause it definitely sounds like your alternator. Hooking up a voltmeter at the battery terminals you should get 14.2 or a little better idling without a bunch of stuff turned on. (basically a bench test on the car.) Wave form will tell you whether any diodes have gone out, but if you aren't getting the correct voltage, does it matter? If it were the battery, then you would have proper voltage readings when the car is idling.
10-19-2016, 05:40 PM
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Fair point. I'd just like to be sure before I go in there. Increasingly, this seems intermittent--sometimes it's 14.2V. But of course that just means worse news is coming! I haven't yet found a pattern, with heat or length of drive. However, yes, I think it may be time for an alternator.