N421LV

After four years of ownership bliss, I guess I was overdue for an electrical gremlin:

** '91 GT with no known history of electrical issues

** Two months ago I replaced the battery since it was having trouble holding a charge. Battery dealer confirmed the old battery had a bad cell. Put in the new battery and everything's back to normal. Until....

** Last week I got out of the car, locked it, and as I am walking away, the factory alarm goes off (a first for me). Happens again the next day. After reading the owner's manual again, I notice that sometimes when I lock the car, the LED's in the lock plungers don't illuminate. So I think, "must be a bad alarm contact somewhere"

** I then go out of town for four days (car is home in my garage). Today I try to start the engine, and my two month old Interstate battery is totally, completely dead. So dead, that it will not accept a charge from my Battery Tender. I remove the battery from the car and it still will not take a charge.

I can't help but think the alarm problem has lead to the stone-dead battery. I'm no electrical genius, but would be interested in attempting some additional troubleshooting before turning it over to a pro. Any advice would be very much appreciated.

Kurt

WallyP

While it is unusual, it is not unknown for a battery (new or otherwise) to have a broken internal connector. I have had two in the last five years.

The battery should be covered under warranty - replace it and see if the problem reoccurs.

The alarm/locking problem is most commonly inside the doors on the door lock switches/connections. Search should give you several threads with similar problems.

VehiGAZ

I think you are not recharging the battery for some reason. Check your ground strap CAREFULLY for good connections. I had similar problems when the battery disconnect switch the PO put in (one of those green thumb-wheel jobs) was not screwed down tightly and led to very poor battery recharging.

Good luck!

dr bob

With the battery still out of the car, try charging it with a real battery charger rather than the battery tender. My maintainers won't charge a battery with low terminal voltage, won't even try. Perhaps yours is the same. Even an inexpensive charger from Wal-Mart will do the job for you. Plus a ~6-10 amp charger is pretty handy to have.

On the door locks-- my car had similar symptoms when it was having battery charge/low voltage problems. Got to a point where locking the driver's door with the key would not lock the other door as it normally would. Fixing the charging issue cured that and several other symptoms.

So, order of business will be to recharge the battery with a real charger. Charging energy is less than 100% efficient, so a battery might need ten hours with a 6 amp charge current to recover 40 amp-hours of capacity. Verify that the terminal voltage at the battery is 12.5V or better after charging and then resting a while (like 15-30 mins). If it recovers OK, put it back in the car. Start the car, and check the voltage again at the battery with your meter. It should be at 13.5V or greater with just the normal stuff drawing current at idle. If it's less, you'll want to find out why. Might be poor connections, bad ground connections at the battery and/or the engine, and may also be poor connections in the battery cable connections at the alternator, starter, or battery positive post.

Could also be the alternator belt slipping. The belt needs to be tighter than most folks realize. Thumb pressure should move the belt 1/2 a belt thickness middle of span; That's a pretty thin belt, so it needs to be pretty darn tight. A slipping alternator belt doesn't squeel the way a V-belt might, so it could easily be slipping and you wouldn't hear anything. If the belt is older, a new one is inexpensive, and since it's the outer belt on the crank pulley it's relatively simple to put a new one on there. Be sure to retension a new belt after a few hundred miles or it will slip too.

Or the alternator might be damaged or worn out. There are rebuilts available from the usual sources. The brush and regulator assembly is easy to replace without disassembling the alternator if worn brushes are the problem, but usually by the time the brushes are worn, the bearings are due and the slip rings on the armature need attention too. The regulator assy is available from 928 Int'l for about $75 last time I looked.

Post your results please.

VehiGAZ

Yay! I got one right!!

While I am certain the symptoms you described are being caused by a recharging problem, you must also check to see if you have an electrical draw when the car is shut off. It should be well under 50 mA with everything shut off and locked up.

If there is a problem with the alarm (or other device) drawing too much power, that could be a concurrent and exacerbating problem to the poor recharging.

Good luck!!!

Calgary Ole

Have you done any work to the car lately? Is everything working in the car,lights guauges etc? I recently developed a battery drain that would cause my alarm to go off (usually at 3 AM). After alot of testing and troubleshooting, I traced it to the cigar lighter power wire had come off and shorting. I had installed a stereo a couple months before and must not have attatched the power wire properly and it took awhile to dislodge.

rexpontius

Perhaps your problem is similar to my Central Locking problem, which also slowly but surely drained the battery.
In my car there was a broken wire which tells the central locking system if the door is locked or not (wire gets a ground when the door is locked). Because this wire was broken it sometimes was not possible to lock the doors (it would unlock immediately after locking). This also resulted in the interior lights and warning lights (red lights in the door) to remain on, and so draining the battery.

I am by no means a 928 expert yet, but perhaps it is worth checking out. You can easily check the current draw with the interior light relais removed / not removed.

good luck

N421LV

Thanks for all the responses so far!

I took the battery back to my dealer today and he thinks it can be recharged (like what dr bob said) and will do it on their whiz-bang unit overnight for me....the voltage was down to 5 volts! The alarm issue was the only unusual symptom I observed before the dead battery. Wouldn't a charging issue probably trigger one or more idiot lights on the dash? As for recent work, nothing of significance over the last six months or so. Rexpontius, the central locking system seemed to be working normally. It was more that the alarm did not seem to be arming properly, but I will try it again and watch closely after the battery is installed.

When I get the battery back tomorrow I will put it in and try to get some measurements.

Mrmerlin

you probably need new brushes in the alternatorr

Alan

Sorry but bad news - when a battery is discharged that badly it never really comes back fully...

It may be adequate for a while but it will have lost a lot of its total charge capacity and will never fully recover - more deep discharges will have cumulative effects. No matter how long you charge it it will not achieve the equivalent of its initiall fully charged state.

After charging I'd ask for it to be full load tested and see if it still looks good. BTW A full load tester is not a handheld gizmo - its usually a big unit in a mesh box with a fan bolted to the ground.

Yes the technician will try to tell you his little handheld voltage tester is the modern equivalent... blah blah blah... he's either lying to you or stupid - either way - wrong.

If they don't have a real load tester go elsewhere. If it fails on the load tester get it replaced and figure out what's killing your batteries before you kill the new one too... (meanwhile disconnect - just 1 deep discharge cycle is very bad news...)

Alan

N421LV

I'm with you on the battery, Alan. I was planning on replacing it once the real problem is found. I was hoping initially it might all be chalked up to a defective new battery, but it doesn't look like I'm gonna get off that easily.

928 at last

I've played this game before too. (Not on one our cars, but...)
First thing to check is a defective battery from someone other than the people you bought it from. Get a print-out or written summary of the results. And yes, Alan's correct (As usual).
The hand held unit isn't quite up to the task......
If it really isn't the battery itself. grounds.......
Then the actual alarm circuit.

taffelman

As for the battery drain check that both the interior lights on the doors goes off after you lock the car. It's easy to accidentally hit the light switch with your leg when getting in/out of the car so that it stays on all the time.

Worth a check before you start to rip out fuses and relays.

SQLGuy

The main battery killer I had problems with in my '85 was the defog/defrost switch/relay (can't remember whether it was actually the switch or the relay that was at fault in the end). Anyway, you might want to make sure that the defog/defrost is really turning off when you turn off the car.

Mrmerlin

after you put the new battery ion then test the voltage that the charging system is providing my guess is its not enough to charge the battery and with it not getting charged up properly it will soon die