New Battery Keeps Dying
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Elder User
Joined: Mar 2008
Posts: 816
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From: Sandy Hook, CT
New Battery Keeps Dying
I just put in a new battery (Interstate) on my 96 250 5.8. It seems to lose charge overnight. Obviously it's a drain somewhere. I hate hunting down electrical gremlins. Any advice on where to start? Could this simply be a faulty alternator? In other words, would a bad alt kill the batt just by being hooked up to it? Thanks for any input!
Roger
Roger
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It could. Bad diode(s). Simple diagnostics is easy (and don't hafta get dirty, or smash fingers!) Seriously a lot of it is find out where the problem isn't, a voltmeter can take you pretty far.
"Sometimes a bad alternator diode can cause a car battery to run down. A good diode should only pass current in one direction. If it leaks current in the opposite direction, it may keep the charging circuit on when the engine is not running, causing the battery to run down. This kind of problem can be diagnosed several ways. If your voltmeter has an AC (alternating current) scale, switch to that scale and observe the charging voltage with the engine running. If the meter shows any AC voltage, one or more diodes are leaking and the alternator needs to be replaced. The alternator's output can also be observed as a waveform on a digital storage oscilloscope (DSO) or an alternator tester that measures ripple voltage to detect this kind of problem. Or, just disconnect the alternator overnight and see if the battery stills run down. If the battery drain stops, you have found the problem. Replace the alternator."
http://www.aa1car.com/library/battery_runs_down.htm
"Sometimes a bad alternator diode can cause a car battery to run down. A good diode should only pass current in one direction. If it leaks current in the opposite direction, it may keep the charging circuit on when the engine is not running, causing the battery to run down. This kind of problem can be diagnosed several ways. If your voltmeter has an AC (alternating current) scale, switch to that scale and observe the charging voltage with the engine running. If the meter shows any AC voltage, one or more diodes are leaking and the alternator needs to be replaced. The alternator's output can also be observed as a waveform on a digital storage oscilloscope (DSO) or an alternator tester that measures ripple voltage to detect this kind of problem. Or, just disconnect the alternator overnight and see if the battery stills run down. If the battery drain stops, you have found the problem. Replace the alternator."
http://www.aa1car.com/library/battery_runs_down.htm
Junior User
Joined: Jul 2007
Posts: 55
Likes: 1
From: norfolk, va.
On older cars and trucks, you can put a test light between battery neg. and the neg. cable. Remove cable , clip one end on neg battery term. and other end on cable. Light should come on. Start pulling fuses till light dims or goes out. When light goes out, check that circuit that the fuse goes to. Just something to try. Good luck.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
On older cars and trucks, you can put a test light between battery neg. and the neg. cable. Remove cable , clip one end on neg battery term. and other end on cable. Light should come on. Start pulling fuses till light dims or goes out. When light goes out, check that circuit that the fuse goes to. Just something to try. Good luck.
Substitute an ammeter or current probe then you have a viable diagnostic tool.
Posting Guru
Joined: Jan 2015
Posts: 1,001
Likes: 8
From: NC Mountains
A low amp probe around the battery cable will tell you the amount of draw. To narrow it down to a circuit you can pull fuses one at a time to see which one eliminates the draw.
http://www.diagnosticnews.com/parasitic-battery-drains/
http://www.diagnosticnews.com/parasitic-battery-drains/
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wolverineflight31
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