Well my battery is only 5 months old, pep boys battery, and I just had my alternator replaced about a month ago, since I was told it was bad, and the one I bought was used, but was supposedly tested before being sent to me, from an ebay seller, and the first weekend it was on, I didnt drive my car, and monday when I went in to go start it for work, the car cranked once, and was dead, and battery was showing under 9v, so i jumped it that afternoon, and it was fine.

That afternoon, I took my car to walmart to have them check the battery and alternator, and the guy told me the battery was bad, so I took it back to pep boys and had them test it, and they said it was good, so im confused here? The problem is when I start the car in the morning, its only showing 13-13.5v on my SAFC, and after driving for a while, it gradually gets lower and lower, sometimes even into 11v, and the car starts running rough and idles low, and I dont know what the problem could be.

I didnt install it myself, I had my job do it, but i dont know how they could have did it wrong, and the belt is tight, I just put a crank pulley on, and made sure it was tight, but that didnt help nothing, and checked the 120amp alternator fuse, and its fine, so what else could be draining the battery like that?

While running, if the battery voltage is dropping then the alternator is garbage. Autozone and many parts stores can load test an alternator. They spin it to make sure it puts out 14v and tell you its ok. They also do not have the tools to test the A/C ripple out of the alternator either. That test determines the status of the rectifier.

Think logically about this, if the Alternator output is 14v volts then the alternator must be good right? What if it only puts out 14v at 20 amps and the Vehicle requires 30amps just to operate? What is going to happen to your battery?


WALMART tests.... I am sure they use the older style load testing equipment to test batteries. These require the battery to have a full charge. The way the test works i syou apply 1/2 the CCA of the battery as a load and see how low the voltage drops. Voltage drops below 10.8 volts then the battery is no good. What is the result if the battery is only charged to 11volts because you were driving on it and the vehicle was consuming power from the battery? 1/2 the CCa should drop it at least 1 volt.

The latest testing equipment in the industry actually tests batties based on impedance of the cells and a low frequency test. These testers only require the battery to have at least 1 volt charge on it. Trust me on this, I own one.

No idea what pep boys uses, could be the newer equipment since they are more of an automotive chain.

Terry

thanks terry, i had already emailed the guy who i bought the alternator from, and he said if its bad, he can send me another one, so i guess i should have him send me one? but i spent 70 on gettin it installed by my job since im a lazy ass, plus the mechanic said it was a pain in the ass, maybe i can get the guy to pay me for it as well?

I don't know about you guys, but i love my car, and the only reason i take it to wal mart, is to buy cheap toilet paper and fake coca cola......when it comes to my car i go to shops where people care about what they do.

the battery is used to crank the car, once started, the alternator does all le work...so dropping voltage while running = crappy alternator but good battery

Quit your job
Sell your car
Get on a plane
Surf and party
Fall in love
Never come back...

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)

-Chris
1999 Eclipse T-GS


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