Battery keeps dying!!!

[dj393]

HELP!! I am losing my mind! I have been working on the following electrical problem for months and am getting nowhere!
76 911S Targa – Something seems to be draining the battery. Can charge battery to full (which never seems to test above 12V) Car will start a couple of times then battery is dead! Have removed alternator and tested and it was ok, voltage regulator is ok, starter is ok, have replaced generator bulb, have replaced battery, have checked ground strap and it is tight to frame. I bought Wayne’s book and went through the fuses with a voltmeter and couldn’t find where the draw was coming from. I have done everything I can think of (short of taking it to my mechanic which will cost a fortune!) Not sure what else to check. After I removed the alternator and replaced it, the car seemed to be ok for a couple of weeks and now it’s doing the same thing again. I noticed it first started after I washed the underside of the car, but I didn’t see anything unusual when I was underneath the car checking the starter. Are there any other Tulsa, OK pelicans out there?!?! HELP!!!

[singpilot]

dj;

Have you changed anything in the stereo system right before this started? The electric antenna is a likely culprit if you have one.

Interior lights? I know it sounds stupid, but I had one on and didn't see it. The switch was barely making contact, but enuf to slowly discharge the batt. Cycle all the switches.

First thing in the morning, go feel the relays. Is one warm? I have heard that unplugging the all the relays when parked for a day or two might start a way to track down the source.

When you pull your key out of the ignition after a day of driving, is the key warm? Might be a switch going bad. If you leave the key in the ign, even with it off, does the radio stay on? Sometimes it's supposed to, but it might be sticking the other way too. I had a sattelite antenna (XM radio) that was (unknown to me) wired to stay on so the menus could download all the time. Had to rework that one.

Keep looking, you'll find it. Let us know.


EDIT: I just noticed you said even after a full charge, you never get over 12v. That could be it. A bad cell in the batt will act like that. Take the batt out and have it tested (McParts, Kragen, Sears) The test is free. Take it charged for the test.

[Wil Ferch]

First of all..... 12V is not fully charged.

I'll repeat an earlier post response here:

Guys:
Look at the original post, and now chew on this:
- normal "full" charge of battery should be 12.6 volts.
- at 12.4 volts..you're at 3/4 charge
- at 12.2 volts, you're likely at 50% or less than full charge.
- at 12 volts....25% of full charge
- battery is between 0 and 25% charge at high 11 volts.

Yep...the profile drops THAT fast !

This should be a hint of what's going on...



-- Wil Ferch

[vash]

i would start with the most obvious and free. maybe the new battery is bad. this happened on my truck and i refused to believe it. i wasted $340 dollars before i went to get the battery tested. it was for some voodoo reason "self draining". i got a new battery, and called the repair shop and *****ed them out to make me feel better. they promised me, they fixed the problem, when in fact they saw my brand new battery and assumed it was good too. and they changed some wiring harness stuff instead. i took the bad battery and charged it up, when i put a voltmeter to it, i could see the volts drop before my eyes. granted, i am very weak with electrical stuff. just my two cents. good luck

[WERK I]

One way to eliminate the battery vs. the electrical system in the car is to take one of the battery cables off the battery and charge the battery back to full charge. Then attempt to hook the disconnected cable back on the battery(make sure the ignition is in the "off" position). If you see an ark when you connect the cable back up, you got a short somewhere. I more accurate method would be to use a digital Volt-Ohm-Meter with an amp meter built in. With the meter, you would put one lead on the battery terminal and the other on the disconnected battery cable. With the meter in the "Amp" position, you would see exactly how much current is being drawn. In either case, if there is no current draw or arc from connecting the cable, you have a very suspect battery.
If using a meter, and it is drawing current with the ignition off, you can pull one fuse at a time to find the faulty circuit. Check the meter each time you pull a fuse. When the meter goes to zero, that's your faulty circuit.
Good luck

[Jerome Ryals]

I'm in the middle of the same problem with one of my 912's, installed a battery disconnect (green knob battery disconnect) until I can track down every possible source. Before I was killing new good batteries in two weeks at least with the disconnect I have three months on this battery with no recharge. I have no idea where the source is to the problem but I look through different wiring parts every weekend.

[Paulporsche]

Dj393,

I know you said you checked for current draws at the fusebox, but many here have noted that their trunk light remained on all the time, causing a battery drain.

Just another thing to try (maybe again).

Paul

[warment]

I second the trunk light.

I had a pesky battery drain on my 73 from the AC blower motor. I took out the motor and have not had any problems at all.

Bill

[joehahn]

Dave, check out this pic:



I read your post and recognized the arcing phenomenon as I have that everytime I attach ground. It is "tiny" spark and it does not recur after I touch ground lead and remove it and touch it again. I attached the ampmeter the way you said and it shows 00.0 and occasionally a 00.1 for a split second. Does that mean I have short somewhere or is that tiny bit of juice ok?

joe 68 L

[WERK I]

Hi Joe,
Well, .1Amps is 100milliamps and with that kind of drain, it would take days to drain the battery. I think our batteries are typically rated at about 800 Amp/Hours, so if you do the math......that's a long time. Do you have a anti theft device, a radio that is "live"(you can turn it on without the ignition key), or automatic antenna?
Another thing to check is check the voltage across the battery while the engine is running and start switching on all the accessories(headlights, fans, radio, etc.. The regulator should detect the load and keep the battery charging, that is, a voltage always greater than 13.7 volts.

[joehahn]

Radio and clock (and cig lighter) I think are the only things live with key off. I think I am good. Thanks for the cool tip on determining drain.

joe 68 L

[WERK I]

Joe,
The only other thing I can think of, outside of the batery, is the starter/selenoid. I have never heard of this, but I suppose it is possible, for the selenoid to stick and stay on after the engine has started. But I would think you would hear the whine of the starter motor while the engine is running. That would draw a lot of Amps and drain the battery in no time.
That small amount of arcing that you see when you first attach it to the battery, is just the clock sucking up a small amount of juice. Mine does that as well. If you had a major short somewhere, you would hear more like a crack when you attached the cable. As always, be careful when doing these simple experiments. Remember, it's not the voltage that will hurt you, it's the amperage.

[joehahn]

whoa whoa whoa, don't get too technical on me now. It was a puzzle just trying to get the right setting on the meter thing! The only thing I try to remember is the old story about "touching a wrench to both battery terminals at the same time will cause the wrench to melt, swarm of locusts, armageddon, etc". That's about the extent of my electrical knowledge!

thanks again,

joe

[Lorenfb]

Any draw greater than 50 to 60 ma really starts to shorten the good cranking
voltage needed. Less than 100 ma should allow good cranking within a 10 day
internal without any charging. Even at the low draw of 50 to 60 ma, the battery
will require trickle-charging after 2 to 3 weeks.

[Early_S_Man]

Whoa, Dave ... you are only off by one order of magnitude on the high side!!!

Automotive batteries are usually in the 30 - 100 Amp-Hr range ... Miata/Honda to big American V-8 ...

100 mA does take several days to drain a battery, though, but a single bulb in the glove box will do it ... or an inferior/defective radio/stereo/alarm design can do it, too!

[WERK I]

Oops! Good catch Warren. I was thinking Cold Cranking Amps, not capacity or reserve.

[Wil Ferch]

No one answered the basic set of questions:
- what is the idle, standby voltage of the battery? Should be 12.6 volts. 12 volts is not "fully charged" and would hint to a bad battery if you find you can;t climb over 12.0 during a charge.
- take the negative lead off the battery...set your meter to milli-amps ( mA)...and put one probe on the neg post and another on the black ( disconnected) ground cable. Measure mA. If high ( 60-400 mA)....then remove/reinstall one fuse....one after another...until the value comes down. The problem will be in "that" circuit. Your problem then will be to understand all the items on "that" circuit. At least you'd have it narrowed down.
---Wil

[Lorenfb]

"- take the negative lead off the battery...set your meter to milli-amps ( mA)...and put one probe on the neg post and another on the black ( disconnected) ground cable. Measure mA"

Or the positive lead, it doesn't really matter. Electrons flow in either case.

[911pcars]

Be aware that if you have a typical lead-acid, open cell battery, explosive hydrogen gas is created during charging. Thus, do not create any sparks around the battery, especially during charging.

I would suggest connecting a test ammeter to the ground side of the battery. Same current, but a little safer on this side of the circuit.

Sherwood

[Wil Ferch]

True....but it's a bit safer to get into this habit if for some reason you lose control of a "negative" lead and it falls onto the (steel) body. Different story if you play with the big red wire this way ...no ?
---Wil