Way to test battery for shorted cell?

Jared at Pelican Parts · 02-09-2006, 06:19 PM

Ok, here's the thing, I need to test a battery tonight (optima) to see if it has a shorted cell. Is there a way to do this with a volt meter? Gotta get it tested tonight, surely theres a way to check it

slakjaw · 02-09-2006, 06:39 PM

is this a sealed battery?

slakjaw · 02-09-2006, 06:50 PM

If it is not a sealed batt. You can open it up and put one of your test leads down into the acid. You can measure voltage per cell that way. They should all have about the same amount.

Jared at Pelican Parts · 02-09-2006, 06:55 PM

Optima, sealed battery

I have seen people just hook some kind of unit up to it in th past that takes 1 sec to check it, anyone know what that is?

slakjaw · 02-09-2006, 07:00 PM

Yes,

Most shops have one. I cannot remember what the hell we used to call it though. I know it had the strap-on brand name.

NAPA sells battery annalyzers. Maybe check there?????

Jared at Pelican Parts · 02-09-2006, 07:07 PM

I dont have that option, I have to test it tonight. I live out in the boonies.

No, i dont have another battery to use

pwd72s · 02-09-2006, 07:20 PM

I believe it's called a load tester...a load, or draw placed on the battery, then voltage drop is measured. Maybe you could get a voltage read-out when trying to start the car?

Jared at Pelican Parts · 02-09-2006, 07:25 PM

Im thinking its either my alt. or battery

VOltmeter shows 9.7V at the battery terminals, 10.1V with the engine off, but it runs fine? Alt light is dimly lit as well

pwd72s · 07:46 PM

Lowest voltage with engine running? Sounds like alternator to me. Do you have a battery charger? If so, charge the battery, then see if you get 12V or above...should be above 12. A 10V reading on a fully charged battery means a dead cell. But your battery may merely be drained because of a failed alternator...(edit) I wish some of the electrical experts here would weigh in, I'm generally terrible with electrics when it gets beyond the most basic testing. I'll tell ya one thing though...I'd prefer a dead battery to a dead alternator. (edit again) dimly glowing indicator light also suggests an alternator or voltage regulator problem. If your car is one with an internal voltage regulator you need to pull the alternator anyway.

Jared at Pelican Parts · 02-09-2006, 07:49 PM

has an internal voltage reg.

Both the alt (rebuilt Bosch) and the battery (optima) are three weeks old

Jared at Pelican Parts · 02-09-2006, 08:15 PM

One other thing.

When you turn on the car, all the lights come on, however the dim battery light stays dim and does not illuminate like it used to.

snowman · 08:47 PM

THe battery MUST be 12.7 volts without a load or its bad, period. Car running should be about 14v or alternator isn't working. Could be battery is down because of not being charged, but with absolutely no load it should still be near 12.7V. To be sure, charge the battery, then recheck it, not 12.7 its bad. Alternator could also be bad, ie battery took it out. If you have 12.7 from the recharge start it and it MUST read MORE than 12.7, most likely 14 V or so. If not its the alternator, which usually has everything build in nowdays.

A load test is very simple. Put the voltmeter across the battery, should be 12.7V, turn on headlights, should be more than 10 V without engine running, more like 11.5 to 12 v with a real good battery. Engine is off for the test. If its near 10 V, take off the battery terminals and clean them. Repeat test. If you are seeing something like 10 V your battery is near its end.

Without a volt meter, start the car, turn on the headlights, gas it, the lights MUST brighten a bit, if not alternator is bad. Note this test is only definitive if you have some experience. With good experience I would give it a 99 percent chance of being correct, without experience I would give it a 60/40 chance of being correct. IE better than nothing.

Note the alt light being dimly lit, indicates the alternator is indeed bad, not for sure, but most likely.

The test I have discribed are pretty darn compreshnsive and you will not likely be mislead by them. I am an expert on this subject so. blowing my own horn, I am confident that it will lead you to the correct conclusion. It ain't rocket science, its just a battery and an alternator with built in voltage regulation. You got a 50/50 chance of being right so anyting you do is likely to result in the correct diagnosis.

Jared at Pelican Parts · 02-09-2006, 08:41 PM

Had the same idea about a load on the system, everything was off, except the headlights.

The Saab has no way of turning off the headlights, however i notice that they are running dimmer than usual, as are the information displays inside the car.

Im just wondering what caused this to happen. As I said before, the alt. and Optima are three weeks old. Is it possible I just got a bad rebuilt alternator? Both battery cables to and from the starter/alt. are brand new as well. This just happened, no warning signs or anything. turned the car on, the warning light came on, and the battery light lit up dim. But the car starts up and runs fine??

snowman · 09:01 PM

Its the alternator. Bad rebuild. And its possible to have more than one, ie 2, 3 or even 5 if the same idiot rebuilt all of them. Not real likely but not impossible, I have had it happen on Porsche starters once. Had to go to another source to get a good one.

Note you can check your voltmeter, which can be off, by checking another car. Should give you the results I stated, if not and its just like your car then your voltmeter is off.

This is NOT an nbs approved way of calibrating your voltmeter, but in the boonies, its ok.

Jared at Pelican Parts · 02-09-2006, 09:07 PM

It's a Fluke, so I doubt it's off.

This is exactly what I didnt want to hear. Good news is that I have a lifetime warranty on the alternator, bad news is removing it, driving a long ways to the auto parts store and re-installing it.

snowman · 02-09-2006, 09:37 PM

A lot of autoparts stores have alternate sources for the same parts. Sometimes they have a "premium" source. Ask for a differen't source for your replacement, sometimes it even cost a few bucks more, but can be worth it. If your in the boonies, ask for a remanufactured part, not a rebuilt one. Cost is not so much an object with the distance and trouble involved.

pwd72s · 02-09-2006, 10:45 PM

Thanks for weighing in Jack...

RANDY P · RANDY P's Garage

I went through 4 alternators in a row in a Caddy once. (Mistake #1 - 83 Coupe DeVille POS GM electronics) - "Ming PO Brand" rebuild from the local Shucks / Kragen (mistake #2) Threw my hands up, took it to a shop, and guess what?

They replaced it with one of their rebuilts - perfect.

rjp

pwd72s · 02-10-2006, 08:12 AM

Must be a luck of the draw thing. I had an alternator die on my Dodge pickemup some years back. A Sunday, so the only parts store open was a Schuck's...spent $29.95 for thir "lifetime guarantee" rebuilt. It's still going, but you can bet that the guarantee is in the glovebox!

Jared at Pelican Parts · 02-10-2006, 12:55 PM

It was the battery.

Did a loadtest, tried recharging, no luck. Just got back from the store where I bought the Optima, they tested it and said it indeed had a shorted cell.

With the engine running, 14V, 13.8 under load.

Good news is that they swapped the Optima with no hassle, not even any paperwork, just handed me a new one.