Battery vs. Alternator
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Battery vs. Alternator
Last week when I finally had a chance to take the car out for a weekend ice cream run it wouldnt start 
. After about 30 mins on the trickle charger it turned right over - however, that only gave me two more starts before it needed to go back on the trickle charger. How do I know if my battery is shot or the alternator has failed?
. After about 30 mins on the trickle charger it turned right over - however, that only gave me two more starts before it needed to go back on the trickle charger. How do I know if my battery is shot or the alternator has failed?
IHI KING!
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From: Nashua, New Hampshire, USA
Charge the battery fully, then remove the charger and check the battery voltage. It should be about 12.5v. If its below that, then you need a new battery. Then start the car, with the engine idling, check the battery voltage again, it should be 13.5v. If the its below 13, then your battery is not charging. Check your battery connections and grounds for corrosion. If all of the connections are clean and solid then I would suspect you had a faulty alternator.
Nordschleife Master
Joined: Feb 2011
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From: Deep Downtown Carrier, OK
+964 on the above, however....
Never embark on a journey such as this without first verifying that all leads and grounds are correct. By verify, I mean pull, clean and re-make.
Never embark on a journey such as this without first verifying that all leads and grounds are correct. By verify, I mean pull, clean and re-make.
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Took the battery to Autozone - they tested it and verified 100% charged. Returned the battery to the car and took the car to Autozone - they claim that the battery was charging from the alternator? I havent done any mods in the past year; is it possible something is draining the battery when not running? OR I may have had the hood open just enough while on the charger to leave the hood light on so I wasnt getting a full charge - but wouldnt the alternator complete the chargeing process once the car is running?
IHI KING!
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Joined: Aug 2001
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From: Nashua, New Hampshire, USA
You could have a current drain. Look for the obvious, trunk and engine compartment lights, sticking door switches keeping the interior light on, etc. If those are ok, then the next step is a bit more involved where you use a VOM and start pulling fuses one a time.
Burning Brakes
Joined: Jun 2002
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From: Seattle
.... is it possible something is draining the battery when not running? OR I may have had the hood open just enough while on the charger to leave the hood light on so I wasnt getting a full charge - but wouldnt the alternator complete the chargeing process once the car is running?
It is very common to have a battery drain somewhere - and not too difficult to determine, if you have a multimeter.
As for the hood being open, yes, this can cause a drain. Even if you have removed the hood light, I have observed an 80mA drain in my car when the hood is open. No idea why. Now I always shut my hood when charging, and it doesn't seem to pinch the small wires to my charger.
Also, I agree that your alternator should be charging your battery completely - as long as you drive it for long enough. I'm not certain, but idle may not be enough to charge quickly or completely.
