How do you determine if a battery is good?

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  #1  
Old 02-18-10, 12:31 PM
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How do you determine if a battery is good?

I put a new battery in my mothers car last summer. 3 weeks ago ( New England winter) it wouldn't start. She called AAA and they said the battery was bad and offered to replace it with a new one. I figured they were just trying to sell a widow a battery since I just put a new one in 8 months ago. Could this battery be shot already? She didn't replace it. I figured that because she doesn't drive it much the car alarm and others things drain the battery. She called me yesterday and said it wouldn't start again. I am going to go over there and charge the battery in the car and after it is charged I will hook up a multi meter and check to see that the alternator is providing enough output when the car is running ( 13.8v to 14.5V) and turn on the headlights and blower to see that it stays there after an initial drop. I was wondering how I can check the battery if it is bad. I don't mean how to check that it is dead as I can do that with the volt meter.
 
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Old 02-18-10, 12:47 PM
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Basically after a full charge with a trickle charger or say 20 miles of driving...the battery should have about 12.5V (higher immediately after finishing charging) and the electrolyte should be in the "good" or fully charged" range when checked with a hydrometer. It should maintain those states for at least 24 hrs...if it does..it's prob just fine and just needs to be driven more..or have a battery maintainer. They make solar maintainers that work..but are kinda pricey.

And yes..the alarm and other electronics can discharge a battery pretty quickly. Many of the batteries in new cars have been downsized to save weight and space and are just barely adequate under ideal circumstances.
 
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Old 02-18-10, 12:51 PM
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So after It is charged overnight it should show twelve volts with a hydrometer? If its a sealed battery I can hook up a voltmeter to it and if it reads 12.5 v that means it was able to take the charge and is good?
 
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Old 02-18-10, 12:56 PM
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Check the wiki entry for "car battery"...everything you need is there....

EDIT Hydrometer is used to measure the specific gravity of the electrolyte. If it stays at that voltage..yes..it should be fine and just needs to be driven more and longer.

Sorry if you read before the edit...wasn't being abrupt...didn't see that you had posted.
 
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Old 02-18-10, 02:30 PM
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I don't know what they would cost elsewhere but years ago I bought a load tester from harbor freight and salvage and it's easy to use and lets you know how the battery responds to a load.
 
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Old 02-18-10, 05:38 PM
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Less than a year old? Can you say warranty.
 
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Old 02-18-10, 06:46 PM
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I have to agree with marksr about the load tester,, If you don't want to buy one, take the battery (or car with the battery in it) to any garage & ask them to load test it for you;; Check the charging voltage as you suggested & just for a goof, clean & tighten the connections... Roger
 
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Old 02-18-10, 07:29 PM
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I take it to Auto Zone. Their computerized tester seems best if you get someone who actually knows how to use it. The test is free. I do not take it to ORiley because they use the simple load tester which failed to detect a a battery that was only taking a surface charge. I would never take a battery to PEP Boys because the only time I did they said it was bad but only after I had bought a new battery did I figure out it was the alternator.
 
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Old 02-19-10, 05:47 AM
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Have to agree with Goldstar. That battery will be under warranty. Just take it out and carry it back where it was bought (or drive it when it starts) and let them test it for free and replace it if bad.

I would certainly not buy a battery from an auto club guy (I've seen what they charge).
 
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Old 02-19-10, 01:53 PM
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Modern vehicles have electronic things with memory and these constantly use a small amount of electricity.

I have a truck which I don't drive much in the winter and the battery dies down after several weeks of not starting it.

Also cold weather makes a battery not work as good.

So charge it overnight and it should be fine.

Then to keep my battery charged in my truck, I got a solar battery trickle charger. This you plug into the cigarette lighter. You need to make sure the cigarette lighter works with the ignition switch off for this to work. And you can get these at some auto parts stores or walmart may have them in the automotive section.

FYI - My truck battery will read about 12.00 volts DC with a multimeter after it has sat for a few weeks without being driven. But it will read more than 12.65 volts after charging the battery.
 
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Old 02-22-10, 07:15 PM
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My FIL has a Lincon town car that he don't use much and ends up having to jump it. I set him up with a trickle charger. 12v 1000ma. I told him to put it on once a week for a day or two. I have a van with the orig. batt. it's a 2000 ten yrs old. I always make sure I put a good charge into the batt. In the winter when the lights,wipers,defroster/heater are on I turn things off and let it run a few min. to keep the batt up. I would say if the alt. is putting up around 14- 14.5 and the battery is above 12v after a day or two It just does'nt get run enough to charge the batt. These newer car with automatic lights, heat ect ect need big altenators to keep up and charge at the same time.
 

Last edited by e150club; 02-22-10 at 07:39 PM.
  #12  
Old 02-23-10, 08:15 PM
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you can test the batter to see if it needs to be replaced.
 
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Old 02-23-10, 08:33 PM
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A garage, dealership, or parts store that has a battery load tester can quickly tell you the batteries condition.
 
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Old 02-23-10, 08:36 PM
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..... but don't forget a battery should be fully charged [if it will accept a charge] before you test it.
 
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