help, my battery keeeps going dead

mustangLX92 · 09-08-2001, 09:19 AM

My battery keeps going dead. How can I tell if it has something to do with my alternator or if it is just a bad battery?

1SILLYGT · 09-08-2001, 10:40 AM

While your car is running disconnect your positive battery terminal. If the car dies it is you alternator. If not just try cleaning your terminal connections

------------------
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mustangLX92 · 09-08-2001, 10:50 AM

If my car is still running when i disconnect the positive cable then I have a bad battery. Right?

84LX89GT · 09-08-2001, 07:12 PM

that is correct mustangLX92, i also heard a neat trick from someone on this board (don't remember who...) anyways, he recommended putting a screwdriver up to the back of the alternator and seeing if it's drawn to it. If it is, the alternator is good because it creates a magnetic field from the current. Good luck,

Unit 5302 · 09-08-2001, 09:07 PM

You can also check to see how bad/good it is by using a multitester while the car is running. Negative to the negative post, positive to positive and setting the voltage to 30 on a standard sweep multitester or just use a digital unit.

hubiev_89lx · 09-09-2001, 12:34 PM

Here is some info that I got off the net a while ago and have never verified, but it seems to make sense.

If your battery keeps going dead in a day or two, and you want to locate a drain, here's what you need to do:
Get a test light, and disconnect the negative battery cable. Hook the aligator clip from the test light to the negative battery cable end, and touch the test light probe tip to the negative battery post. If it lights up, you have a drain somewhere. If this is the case, you then need a helper to hold the test light probe to the negative battery post while you remove fuses from the fuse box, one at a time. When the light goes out, make a note of which fuse it was that you pulled out. That is the circuit with the drain. You can then check and see what accessories are hooked up to that circuit and start checking them out by disconnecting them, one at a time, just like you did for the fuse. The one that gets the light to go out is the problem child.

Like I said I have never had to use it, but it make sense. Good luck.

PKRWUD · 09-09-2001, 12:45 PM

Hehe, I recognize that, word for word. Where on the net did you find it?

Take care
~Chris

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Mach 1 · 09-09-2001, 04:19 PM

What about the radio clock that has constant power for memory? This will appear as a drain, right? But its not the problem, so I would think that would throw you off, as well as any other circuits that are powered with the ignition switch in the off position.

mustangLX92 · 09-09-2001, 04:39 PM

While my car was running i disconnected the positive battery cable and my car died. I also held a screwdriver to the back of the alternator and it stuck to it. do i have a bad alternator? is removing the positve battery cable a reliable way to determine alternator problems?

Thanks for all the input.

Unit 5302 · 09-09-2001, 05:11 PM

I have found most of the time a severe drain on the battery that will kill it in 1 or two days is the internal rectifier in the alternator. I beleive GM refers to this device as a diode trio. It allows current to flow one way only. If it is broken it will allow the alternator to constantly drain the battery when not being run.

I would bet on the alternator, but if you've killed your battery several times, it will also be weak. A car battery isn't a deep cycle, and they don't like being drained completely.

PKRWUD · 09-09-2001, 07:25 PM

mustangLX92-
As Unit mentioned, repeated draining of your battery will kill it, and that may be part of your problem. I have never been fond of disconnecting the battery from an ECM equipped running vehicle, and am not convinced that the alternator is your problem. If the fusible link between the alternator and the starter relay was bad, the engine would kill when you disconnected the battery. Besides, the screwdriver trick is surprisingly accurate. You need to get a voltmeter, and connect it to your battery. note the reading. Next, start the engine and idle it at 1500 for a minute or two. Observe if the voltage increases. If it doesn't, shut off the engine and connect the voltmeter negative lead to the alternator frame, and the positive voltmeter lead to the alternators output terminal. Start the engine. If the voltage increases now, you have a bad fusible link. You really should have the battery load tested as well to see if the problems you have had have killed any cells.

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

PKRWUD · 09-09-2001, 07:41 PM

Mach1-
A short that is strong enough to drain your battery will cause the test light to be bright, whereas the current required to maintain the clock in your radio would barely light it, if at all. A test light typically requires an amp or more to light up normally, while even the old dash mounted dial clocks didn't require more than 1/8th amp. With newer vehicles having more and more relying on the battery when the key is off, you are almost guaranteed to get a dull light with the test lamp, but a bright light is absolutely a short (or a closed circuit that is supposed to be open). Removing the fuses one at a time until there is a noticable difference follows naturally. This process will save you hours when trying to find an unknown short!

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Mach 1 · 09-10-2001, 02:59 PM

Makes sense, but I use a digital multimeter instead of a test light. Just have to interpret the amp drain, or in your case, the brightness of the light.

PKRWUD · 09-10-2001, 03:45 PM

Oh absolutely! I go nowhere without my Fluke, but alot of people here either don't have a DMM, or don't know how to use one.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-08-2001, 09:19 AM	#1
mustangLX92 Registered Member Join Date: May 2001 Location: Maryland Posts: 138	help, my battery keeeps going dead My battery keeps going dead. How can I tell if it has something to do with my alternator or if it is just a bad battery?

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09-08-2001, 10:40 AM	#2
1SILLYGT Registered Member Join Date: May 1999 Location: sloatsburg NY Posts: 28	While your car is running disconnect your positive battery terminal. If the car dies it is you alternator. If not just try cleaning your terminal connections ------------------ 90 GT shorty headers, flowmaster exhaust, off-road h-pipe, 3.73 gears, hurst short throw shifter, GT-40 heads

09-08-2001, 10:50 AM	#3
mustangLX92 Registered Member Join Date: May 2001 Location: Maryland Posts: 138	If my car is still running when i disconnect the positive cable then I have a bad battery. Right?

09-08-2001, 07:12 PM	#4
84LX89GT Mustangs Join Date: Jul 2000 Posts: 1,938	that is correct mustangLX92, i also heard a neat trick from someone on this board (don't remember who...) anyways, he recommended putting a screwdriver up to the back of the alternator and seeing if it's drawn to it. If it is, the alternator is good because it creates a magnetic field from the current. Good luck,

09-08-2001, 09:07 PM	#5
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	You can also check to see how bad/good it is by using a multitester while the car is running. Negative to the negative post, positive to positive and setting the voltage to 30 on a standard sweep multitester or just use a digital unit.

09-09-2001, 12:34 PM	#6
hubiev_89lx Registered Member Join Date: Apr 2001 Location: London, Ontario, Canada Posts: 8	Here is some info that I got off the net a while ago and have never verified, but it seems to make sense. If your battery keeps going dead in a day or two, and you want to locate a drain, here's what you need to do: Get a test light, and disconnect the negative battery cable. Hook the aligator clip from the test light to the negative battery cable end, and touch the test light probe tip to the negative battery post. If it lights up, you have a drain somewhere. If this is the case, you then need a helper to hold the test light probe to the negative battery post while you remove fuses from the fuse box, one at a time. When the light goes out, make a note of which fuse it was that you pulled out. That is the circuit with the drain. You can then check and see what accessories are hooked up to that circuit and start checking them out by disconnecting them, one at a time, just like you did for the fuse. The one that gets the light to go out is the problem child. Like I said I have never had to use it, but it make sense. Good luck.

09-09-2001, 12:45 PM	#7
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Hehe, I recognize that, word for word. Where on the net did you find it? Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-09-2001, 04:19 PM	#8
Mach 1 Registered Member Join Date: May 1999 Location: Georgia Posts: 3,866	What about the radio clock that has constant power for memory? This will appear as a drain, right? But its not the problem, so I would think that would throw you off, as well as any other circuits that are powered with the ignition switch in the off position.

09-09-2001, 04:39 PM	#9
mustangLX92 Registered Member Join Date: May 2001 Location: Maryland Posts: 138	While my car was running i disconnected the positive battery cable and my car died. I also held a screwdriver to the back of the alternator and it stuck to it. do i have a bad alternator? is removing the positve battery cable a reliable way to determine alternator problems? Thanks for all the input.

09-09-2001, 05:11 PM	#10
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	I have found most of the time a severe drain on the battery that will kill it in 1 or two days is the internal rectifier in the alternator. I beleive GM refers to this device as a diode trio. It allows current to flow one way only. If it is broken it will allow the alternator to constantly drain the battery when not being run. I would bet on the alternator, but if you've killed your battery several times, it will also be weak. A car battery isn't a deep cycle, and they don't like being drained completely.

09-09-2001, 07:25 PM	#11
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	mustangLX92- As Unit mentioned, repeated draining of your battery will kill it, and that may be part of your problem. I have never been fond of disconnecting the battery from an ECM equipped running vehicle, and am not convinced that the alternator is your problem. If the fusible link between the alternator and the starter relay was bad, the engine would kill when you disconnected the battery. Besides, the screwdriver trick is surprisingly accurate. You need to get a voltmeter, and connect it to your battery. note the reading. Next, start the engine and idle it at 1500 for a minute or two. Observe if the voltage increases. If it doesn't, shut off the engine and connect the voltmeter negative lead to the alternator frame, and the positive voltmeter lead to the alternators output terminal. Start the engine. If the voltage increases now, you have a bad fusible link. You really should have the battery load tested as well to see if the problems you have had have killed any cells. ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-09-2001, 07:41 PM	#12
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Mach1- A short that is strong enough to drain your battery will cause the test light to be bright, whereas the current required to maintain the clock in your radio would barely light it, if at all. A test light typically requires an amp or more to light up normally, while even the old dash mounted dial clocks didn't require more than 1/8th amp. With newer vehicles having more and more relying on the battery when the key is off, you are almost guaranteed to get a dull light with the test lamp, but a bright light is absolutely a short (or a closed circuit that is supposed to be open). Removing the fuses one at a time until there is a noticable difference follows naturally. This process will save you hours when trying to find an unknown short! Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

09-10-2001, 02:59 PM	#13
Mach 1 Registered Member Join Date: May 1999 Location: Georgia Posts: 3,866	Makes sense, but I use a digital multimeter instead of a test light. Just have to interpret the amp drain, or in your case, the brightness of the light.

09-10-2001, 03:45 PM	#14
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Oh absolutely! I go nowhere without my Fluke, but alot of people here either don't have a DMM, or don't know how to use one. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!