low battery, possible cause?

k9handler · 08-24-2006, 12:34 AM

On my way to work today the electronics suddenly went out but the car remained running. I was only 1 block from my work so I drove it on the rest of the way. Under the hood all is normal, no loose connections or crap on the posts. When I attempted to start the car the battery was too low to turn over the engine. I checked the belt for the alternator and it's good. Connected a charger and noticed that it immediatly applied 50 amps so the bettery was very low. I switched it to a manual mode and used 30 amps for 15 minutes and the battery seems to have taken a charge.

I am able to start the car and everything seems fine even after it has been sitting for several hours, guess time will tell what the problem is...what do you guys think? Could the battery have been just low enough that the alternator could not charge it to a proper level? So battery or alternator?

Jim Smolka · 08-24-2006, 03:14 AM

Sounds like the alternator to me... Maybe a bad diode.

Wil Ferch · 10:30 AM

Only way to *really* tell ( I guess) would be if you knew the stand-by voltage ahead of time.

Remember, the curve is rather steep. A fully charged battery is 12.6 volts and you lose 25% ( of full charge) for every 0.2V lower than that. Battery is essentially "flat" at 12.0V or slightly under....

- Wil

911pcars · 08-24-2006, 10:11 AM

"On my way to work today the electronics suddenly went out but the car remained running. "

Can you provide more details? What electronics?

Have you checked charge voltage at the battery with a voltmeter? Should be around 14+ volts. If not, could be the alternator.

Sherwood

CliffBrown · 08-24-2006, 02:19 PM

Cut & Paste from Batterystuff.com

5. Battery Maintenance is an important issue. The battery should be cleaned using a baking soda and water mix; a couple of table spoons to a pint of water. Cable connection needs to be clean and tightened. Many battery problems are caused by dirty and loose connections. A serviceable battery needs to have the fluid level checked. Use only mineral free water. Distilled water is best. Don't overfill battery cells especially in warmer weather. The natural fluid expansion in hot weather will push excess electrolytes from the battery. To prevent corrosion of cables on top post batteries use a small bead of silicon sealer at the base of the post and place a felt battery washer over it. Coat the washer with high temperature grease or petroleum jelly (Vaseline), then place cable on the post and tighten. Coat the exposed cable end with the grease. Most folks don't know that just the gases from the battery condensing on metal parts cause most corrosion.

6. Battery Testing can be done in more than one way. The most popular is measurement of specific gravity and battery voltage. To measure specific gravity buy a temperature compensating hydrometer and measure voltage, use a digital D.C. Voltmeter. A good digital load tester may be a good purchase if you need to test batteries sealed batteries.

You must first have the battery fully charged. The surface charge must be removed before testing. If the battery has been sitting at least several hours (I prefer at least 12 hours) you may begin testing. To remove surface charge the battery must experience a load of 20 amps for 3 plus minutes. Turning on the headlights (high beam) will do the trick. After turning off the lights you are ready to test the battery.

State of Charge Specific Gravity Voltage

100% 1.265 12.7
75% 1.225 12.4
50% 1.190 12.2
25% 1.155 12.0
Discharged 1.120 11.9

*Sulfation of Batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4 (12v Battery) or 6.2 (6 volt battery). Sulfation hardens the battery plates reducing and eventually destroying the ability of the battery to generate Volts and Amps.

Load testing is yet another way of testing a battery. Load test removes amps from a battery much like starting an engine would. A load tester can be purchased at most auto parts stores. Some battery companies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating. For instance, a 500CCA battery would load test at 250 amps for 15 seconds. A load test can only be performed if the battery is near or at full charge.

The results of your testing should be as follows:

Hydrometer readings should not vary more than .05 differences between cells.

Digital Voltmeters should read as the voltage is shown in this document. The sealed AGM and Gel-Cell battery voltage (full charged) will be slightly higher in the 12.8 to 12.9 ranges. If you have voltage readings in the 10.5 volts range on a charged battery, that indicates a shorted cell.

If you have a maintenance free wet cell, the only ways to test are voltmeter and load test. Most of the maintenance free batteries have a built in hydrometer that tells you the condition of 1 cell of 6. You may get a good reading from 1 cell but have a problem with other cells in the battery.

When in doubt about battery testing, call the battery manufacturer. Many batteries sold today have a toll free number to call for help.

k9handler · 08-25-2006, 05:20 AM

Quote:

Originally posted by 911pcars
"On my way to work today the electronics suddenly went out but the car remained running. "

Can you provide more details? What electronics?

Have you checked charge voltage at the battery with a voltmeter? Should be around 14+ volts. If not, could be the alternator.

Sherwood

First the Ipod shut down, then the stereo shut off. Windshield wipers were slow and the turn signals qould not work. The charge yesterday held and I allowed the car to sit here overnight. Today it started with no problems so I guess it's time to check the charge voltage and make sure the alternator is working properly.

Wil Ferch · 08-25-2006, 05:54 AM

Measure voltage across battery terminals when engine is at 2000-3000 rpm. Should be 13.8-14.4 volts or so.

Shouldn't drop much at idle...but can drop a tad.

- Wil

k9handler · 08-25-2006, 08:07 AM

Thanks Wil...I didn't have a volt meter with me but what I did do was start the car and let it idle with the headlamps on and the stereo, fan blower and such on. Within 5 minutes the same thing that occured yesterday....very low battery and would not restart. Charged again and the battery took a charge...so I am thinking alternator.

Wil Ferch · 08-25-2006, 08:22 AM

Smitty:
You may indeed be right...but get yourself a small shirt pocket multi-meter. The one I use folds-up like a credit card holder and cost $28 from Radio Shack. Gotta be somethin' like that in Germany. Herties'..maybe?..or the equivalent to Home depot that I saw there last year ??

- Wil

stlrj · 01:46 PM

A bad battery or one that is not fully charged can make a perfectly good alternator look bad.

Don't learn the hard (expensive) way like I did.

Joe