killing batteries

[911tracker85]

I have an 84 928 and a few weeks ago the battery died. thought maybe I left the door ajar. tried to charge and my charger said bad battery.

about 2 yrs old and still under warranty so took it back. they replaced it.

put that in, car starts and drove it. next day battery dead again. try to charge, dead. took it back, they tested bad so gave me another one.

put in car, starts, drove it. but again next day dead.

another new battery, but now getting resistance as they think my car is killing them. so now on my 3rd battery. I talked to Roger Tyson and he had never heard of a situation where an elec problem with a 928 (or any car) KILLS the battery. drain maybe.

this time after a drive disconnected the battery. this worked for a couple days so left it connected.

next day dead.

so I am believing I am just getting bad batteries. all coming from same shop and all have same date sticker.

I do believe there is a slight draw, if I leave the battery connected and not drive for a month or so it will drain. but in the past could recharge the battery and on my way..... over the winter I will disconnect the battery when I know I will not drive for a while.

anyone know of a situation where a 928 KILLS the battery.

going to try to put one of my other batteries in the car, not correct for a 928. if that keeps a charge for a couple days will just go to a different shop and get another new one.

any ideas or experieneces?

[honerboys]

sounds like a drain on the battery - i had a bad rear hatch switch and it would let the interior lights stay on - which i didn't notice in daytime - would kill battery - but not overnight - if you have a clip on ammeter - put it on the positive battery cable and see what it's drawing with everything off - should be negligible - if it's not remove fuses one at a time until you find the circuit that's pulling the amps - go from there - would be weird to get one bad battery after another - only things i can think of in a 928 that draw when car is off would be clock and radio memory - is your alternator charging when it's running?

[stepson]

Originally Posted by honerboys

sounds like a drain on the battery - i had a bad rear hatch switch and it would let the interior lights stay on - which i didn't notice in daytime - would kill battery - but not overnight - if you have a clip on ammeter - put it on the positive battery cable and see what it's drawing with everything off - should be negligible - if it's not remove fuses one at a time until you find the circuit that's pulling the amps - go from there -

Additionally, if the hatch switch keeps the interior lights on, it's also keeping the Red safety lights in the end of the doors on(or at least that circuit anyway). You can kill that hatch switch by disco'ing the brown/white 2 wire connection to the switch back in the hatch latch area until you get it figured out.

[911tracker85]

I have come to believe I developed a larger draw than in the past. today start down the fuse at a time test.

talking to another mechanic and he asked if they were AGM batteries. yep. he said drain them one time and they die, I know some batteries are like that.

[harborman]

After you turn the car off, put an amp meter between the battery and Plus lead or between the negative side and ground. I would think a 10 amp meter might do, hoping the draw is less than that, but the larger the meter might be better. If the draw is more than an amp, you have something on. I would think it should be much less than 1 amp.

[Bigtoe32067]

A drain wouldn’t kill the battery only discharge it. It should be able to be recharged. Some chargers won’t initiate charge if the battery is completely dead.

I have similar problem in a 911 that will kill the battery Ina day or two and I have to use my old charger to put a little charge in it and then I can hook my new computerized charger to it and it will finish the job.
If I try to use the newer charger it says battery bad and won’t even try to charge. It just says that the battery is bad and shuts itself off.

It sounds like you have a pretty big drain if it kills it overnight. An acceptable drain on a battery is 50-100 milliamperes which is .05 - .1 amp. Anything higher than that means there’s a problem.
You have to let the car sit for about an hour with everything shut off, key out, and doors closed so everything will have enough time to shut down. If you do it too soon like 5 or 10 minutes then you’ll still see some accessory drains that will be mistaken for unwanted draws, these will shut themselves off after time.

I would suggest a battery cutoff switch so you can disconnect the battery electrically from everything once you’re finishEd driving while you’re trying to determine the cause. That a way you won’t keep going through batteries while trying to find the problem because it’ll recharge while you’re driving and stay charged once you disconnect it.

Harborman is correct.
Hook your multimeter up between the negative terminal on the battery and the ground or positive terminal and positive cable to determine the amount of the draw and then start pulling fuses to determine which circuit the drain is in. It’s just a process of elimination from there.

Good luck

[harborman]

Originally Posted by Bigtoe32067

A drain wouldn’t kill the battery only discharge it. It should be able to be recharged. Some chargers won’t initiate charge if the battery is completely dead.

I have similar problem in a 911 that will kill the battery Ina day or two and I have to use my old charger to put a little charge in it and then I can hook my new computerized charger to it and it will finish the job.
If I try to use the newer charger it says battery bad and won’t even try to charge. It just says that the battery is bad and shuts itself off.

It sounds like you have a pretty big drain if it kills it overnight. An acceptable drain on a battery is 50-100 milliamperes which is .05 - .1 amp. Anything higher than that means there’s a problem.
You have to let the car sit for about an hour with everything shut off, key out, and doors closed so everything will have enough time to shut down. If you do it too soon like 5 or 10 minutes then you’ll still see some accessory drains that will be mistaken for unwanted draws, these will shut themselves off after time.

I would suggest a battery cutoff switch so you can disconnect the battery electrically from everything once you’re finishEd driving while you’re trying to determine the cause. That a way you won’t keep going through batteries while trying to find the problem because it’ll recharge while you’re driving and stay charged once you disconnect it.

Harborman is correct.
Hook your multimeter up between the negative terminal on the battery and the ground or positive terminal and positive cable to determine the amount of the draw and then start pulling fuses to determine which circuit the drain is in. It’s just a process of elimination from there.

Good luck

Yes, I was going to say about 100 or 200 milliamps. Maybe what the clock or alarm system draws. If that. I say find the problem, no need for a cut off switch. Sometimes I leave my 928 for a month or two and it starts right up. Put the amp meter on, pull fuses and see which one drops the current draw. Do not try starting the car with the meter installed.

[Bigtoe32067]

I just suggested the cut off switch so he could enjoy driving it if he didn’t have time to tackle it now or if it took some time to track it down.
After you pull the fuse and determine the circuit it gets a little more difficult to trace it to the actual component since some of them aren’t very accessible.

I’m confident he’ll figure it out with all the advice in here.
Good luck to him

[harborman]

Originally Posted by Bigtoe32067

I just suggested the cut off switch so he could enjoy driving it if he didn’t have time to tackle it now or if it took some time to track it down.
After you pull the fuse and determine the circuit it gets a little more difficult to trace it to the actual component since some of them aren’t very accessible.

I’m confident he’ll figure it out with all the advice in here.
Good luck to him

Actually, he could just take off the ground strap which has that finger nut at the rear.

[911tracker85]

thanks for the posts. dont really know about AGM batteries but dont plan to get another....

got it down to the shop to start chasing the draw. one issue I just noticed when taking to the shop is the ALT discharge light is on, even with the key turned off. start the car and the ALT gauge shows a pretty normal reading when driving. Talked to Roger Tyson and he suspects an issue with the voltage reg or something in the ALT. I have a new one on the shelf.

so after checking the ALT, start down the 'whack a mole' process on the fuses.

[honerboys]

i don't think that light should come on with key off no matter how many amps an electrical device is pulling - so the regulator/alternator problem might be the actual reason for the current draw - have you tried pulling fuses to see if that light goes out

[911tracker85]

got a multimeter that shows amps. with alt connected it is drawing almost 5 amps. with alt disconnected just over 1 amp and that is with the courtesy lights on due to hatch being open.

so replace the alt today and go from there.

I know these cars tend to have a small draw but any idea what is normal?

[Cajundaddy]

Yep, the car had 1 or more serious amp draws killing multiple batteries. AGM batteries are fine but any battery taken all the way to zero will be deeply damaged. Same with FLA. Hopefully the alt represents the lion's share but I would test each circuit and record the amperage draw for each to see if there are other problems. Get as close to zero mA loss as you can.

[harborman]

Originally Posted by 911tracker85

got a multimeter that shows amps. with alt connected it is drawing almost 5 amps. with alt disconnected just over 1 amp and that is with the courtesy lights on due to hatch being open.

so replace the alt today and go from there.

I know these cars tend to have a small draw but any idea what is normal?

Just one amp will draw the battery down. Draw should be in the low milliamp range. Enough maybe to keep the clock running and possibly alarm system.

[honerboys]

put my clamp on ammeter on my battery cable - lowest setting it has is 20 amps so it can't measure milliamps very well - but it registered 0 amps - so that means my car just sitting with doors closed is pulling way less than 1 amp - probably a few milliamps - i don't have an alarm so the only things i can think that would be pulling anything are the clock and the radio (memory) - so if you're pulling 5 amps you have a major draw - start pulling fuses

[Bigtoe32067]

50-100 mil amps is acceptable

[911tracker85]

well.....

after trying for a couple weeks I gave up and ordered another alt WITH A NUT. at some point during storage the threads on the Bosch alt got damaged. tried little files, a thread file, dremmel, etc to try to clean them up. I had lost the nut and it appeared to be a M16 x 1.5. I used my tap and die tool to measure the thread pitch.

when the M16 would not fit and it appeared to be too small I then suspected it may be an M18. finally got one and it is too big.

so got the new alt from Roger. no idea what it is but the nut on the new alt fit the old one fine. and I could not get an M16 on. so this must be some unusual size.

with the new alt on and the hatch closed so not interior lights on it only draws 48mA.

I just saw another post on the 911 forum where someone had the same experience with a bad alt creating a large draw.

if I had not noticed the alt light I would have spent a lot of time doing whach-a-mole on the fuse panel and never would have found it that way.

so another of the odd situations that can drive us crazy.

[harborman]

Originally Posted by 911tracker85

well.....

after trying for a couple weeks I gave up and ordered another alt WITH A NUT. at some point during storage the threads on the Bosch alt got damaged. tried little files, a thread file, dremmel, etc to try to clean them up. I had lost the nut and it appeared to be a M16 x 1.5. I used my tap and die tool to measure the thread pitch.

when the M16 would not fit and it appeared to be too small I then suspected it may be an M18. finally got one and it is too big.

so got the new alt from Roger. no idea what it is but the nut on the new alt fit the old one fine. and I could not get an M16 on. so this must be some unusual size.

with the new alt on and the hatch closed so not interior lights on it only draws 48mA.

I just saw another post on the 911 forum where someone had the same experience with a bad alt creating a large draw.

if I had not noticed the alt light I would have spent a lot of time doing whach-a-mole on the fuse panel and never would have found it that way.

so another of the odd situations that can drive us crazy.

Glad you finally solved the problem. Thanks for letting everyone know how you fixed it. People sometimes look for advise, but never get back on the solution. Another thing, post your model, year and mileage. May help in the future.

[Danglerb]

I put a battery disconnect switch on the ground strap, but checked this week and the Bosch Platinum battery was dead dead dead, so I think we get the special magic of 928 drains combined with generally lower quality batteries especially is odd sizes.

[harborman]

Originally Posted by Danglerb

I put a battery disconnect switch on the ground strap, but checked this week and the Bosch Platinum battery was dead dead dead, so I think we get the special magic of 928 drains combined with generally lower quality batteries especially is odd sizes.

My 928 sits for days and the battery never goes down to the point the car will not start. You have some kind of short possibly. I have a Walmart battery, probably now 7 years old. Is there another ground wire on your battery? Of course a battery will discharge do to internal resistances over long periods.