Battery Drain (Not A Stang)

[Pearl02]

The car is a 2000 Mitsubishi Eclipse GT. A couple of months ago, I had to put a battery in the car. The battery I replaced was over 2yrs old. That morning the car would just barely start. I used my voltmeter and the the battery was showing 10.9 volts. With the engine running I hd 14.5volts which tell my the alt is good. I drove over to Advanced auto and the guy there said the battery was basically dead. The battery was replaced. 2 days ago the car wouldn't start at all. Again I used my volt meter and the battery was showing 11.5 volts. This time I had to jump it to get it started. We decided to take the car to the local Mitsu dealer. I told the guy that I thought there might be a slow battery drain. I told him according to my scan tool the alt was putting out about 14.4volts. We both agreed that the alt was good and working. Anyway, the dealer couldn't find any evidence of a battery drain. We replaced the battery. This battery was only 2 months old. I know it's possible to have a battery go bad but I like to rule it out. What's the best way to find a slow battery drain? I read several way to do it. My question is, does the computer use any voltage while the car is off? Thanks for the help. Pearl02.

 

[trinity_gt]

Sounds like you've got a parasitic draw in a circuit always connected to the battery. One way to verify this is to use an ammeter: Turn the ignition off. Remove the positive lead from the battery and insert the ammeter between the battery terminal and the positive lead. A few tens of milliamps is to be expected -- generally -- but hundreds of milliamps or more is causes for suspicion. If you see that much, start popping out fuses to see if you can identify the circuit the drain is on.

If there's a parasitic drain, I'm tempted to suspect the alternator, even though it appears to be charging okay. A bad diode in the rectifier bridge may allow current to return to ground through the stator with the engine off but the alt will still charge when running. You might start the drain-diagnosis by disconnecting the stator connection at the alternator to see if the current drops immediately.

 

[wmburns]

Good luck on this as this can be very difficult to trace. +1 on everything above.

Note, there are systems that do use some power all of the time. Further, the car may have timers that stage on/off various loads to conserve power. The various power loads can be very small which will make them difficult to measure. The good news is the draw has to be fairly large to drain a battery over night.

Has there been any changes to the car? Audio install? Alarm install? If so, that is a good place to start.

Many high power amps need a separate signal to turn on/off. In other words, the radio has two power signals. One is switched with the car and the other stays on all of the time. If the amp is wired directly to B+, it will never turn off and drain the battery.

 

[Kilgore Trout]

The car is a 2000 Mitsubishi Eclipse GT.

There is the problem ^

Seriously though you may consider taking it to AutoZone and having the charging system tested for free in the parking lot.

 

[sbelyo]

I had a similar problem in my wife's 99 G20. It drained an Optima Red top down to 11.5 volts. When you would jump it and check the alternator it would put out 13.2 With just the AC on it would kick down to 12.9

So we figured it was the alternator. I let sears test the charging system and they said it was definitely the battery. Since it was an Optima I took it back to the store I got it from and they tested it. After about 10 minutes the machine said the battery was fine. they were able to pull 770 CA at 12.7 volts from it. So I'm still blaming the alternator. I charged up the optima and went to put it back in the car.

That when I noticed the negative battery cable. The terminal had a hairline crack in it and even though it was tight to the post, only half of the terminal was contacting the post. The cable was also grounded in two spots, one on the frame and one on the trans. The ground on the frame was corroded also.

I replaced the cracked terminal, and cleaned the posts and ground points. When I fired it up it was putting out 14.2 volts. Then when I turned on the lights, AC, Defrost, and radio it dropped to 13.1

Now it's been charging/running fine for a month. So check all the connections for cracks, corrosion and tightness etc. etc.

 

[Pearl02]

Sounds like you've got a parasitic draw in a circuit always connected to the battery. One way to verify this is to use an ammeter: Turn the ignition off. Remove the positive lead from the battery and insert the ammeter between the battery terminal and the positive lead. A few tens of milliamps is to be expected -- generally -- but hundreds of milliamps or more is causes for suspicion. If you see that much, start popping out fuses to see if you can identify the circuit the drain is on.

If there's a parasitic drain, I'm tempted to suspect the alternator, even though it appears to be charging okay. A bad diode in the rectifier bridge may allow current to return to ground through the stator with the engine off but the alt will still charge when running. You might start the drain-diagnosis by disconnecting the stator connection at the alternator to see if the current drops immediately.

This is how I was going to start my test. I also thought that the alt might have a bad diode. I check it out. Thanks.

Good luck on this as this can be very difficult to trace. +1 on everything above.

Note, there are systems that do use some power all of the time. Further, the car may have timers that stage on/off various loads to conserve power. The various power loads can be very small which will make them difficult to measure. The good news is the draw has to be fairly large to drain a battery over night.

Has there been any changes to the car? Audio install? Alarm install? If so, that is a good place to start.

Many high power amps need a separate signal to turn on/off. In other words, the radio has two power signals. One is switched with the car and the other stays on all of the time. If the amp is wired directly to B+, it will never turn off and drain the battery.

It has a stock radio with no high power amp. Thanks.

There is the problem ^

Seriously though you may consider taking it to AutoZone and having the charging system tested for free in the parking lot.

The dealer and Advanced auto checked out the charging system. Thanks Kilgore.

I had a similar problem in my wife's 99 G20. It drained an Optima Red top down to 11.5 volts. When you would jump it and check the alternator it would put out 13.2 With just the AC on it would kick down to 12.9

So we figured it was the alternator. I let sears test the charging system and they said it was definitely the battery. Since it was an Optima I took it back to the store I got it from and they tested it. After about 10 minutes the machine said the battery was fine. they were able to pull 770 CA at 12.7 volts from it. So I'm still blaming the alternator. I charged up the optima and went to put it back in the car.

That when I noticed the negative battery cable. The terminal had a hairline crack in it and even though it was tight to the post, only half of the terminal was contacting the post. The cable was also grounded in two spots, one on the frame and one on the trans. The ground on the frame was corroded also.

I replaced the cracked terminal, and cleaned the posts and ground points. When I fired it up it was putting out 14.2 volts. Then when I turned on the lights, AC, Defrost, and radio it dropped to 13.1

Now it's been charging/running fine for a month. So check all the connections for cracks, corrosion and tightness etc. etc.

Didn't think about this one. Will check it out. Thanks. Pearl02.

 

[GDawg]

I like Trinity's response. I had a large drain. Killed one Optima and almost killed a second one. Once the battery drops below 10.5 volt it is getting severly damaged. A few deep cycles on a non-deep cycle battery will kill it.

I tested as suggested. I had bad diodes in my alternator and found drains through my stereo by testing the fuses. Once replacing the alternator, the drain dropped by half. I still have a bit of drain from my after market stereo.

Btw, I do my test through the ground side of the battery...

Milli Amps... .04 amp (40 milli-amps is acceptable... .171 amp is not (171 milli-amps is not) my readings...


:SNSign:

 

[Pearl02]

Just wanted to give you guys a update. I borrowed a DC amp/volt meter from one of the techs I work with. Those guys have all the toys. After doing some testing the car doesn't seem to have a slow battery drain. The amp meter show very little amps being used while the car was turned off. I compared that to my Stang and amp output was about the same. I starting to beleive that my friend didn't close her car door or hatch back good enough. She get's in a hurry and doesn't make sure things a secured. Anyway, it's been a couple of months since this problem occured and everyhting seems ok. Thanks for the input guys. Pearl02.