9 months ago I put a new battery in my car. It failed 3 months later. Under warranty I got a new battery. It failed 3 months later. It has been 3 months and just got my 3rd one. In the last 2 cases the CCA was measured and was shown to be low (rated 775, read 180). Measured voltage at the battery terminals with car off, at idle, and at 3000 RPMs. All within spec. No bulging of the battery case. Tool the car to AutoZone and they tested the charging circuit. All tests passed but I was warned that it is not a very good test. I live in Phoenix where batteries normally last about 2 years.
Was the alternator tested and shown to be charging correctly? Not sure what the charging circuit specifies.
Get one of those voltmeters that plug into the lighter socket and drive around with that. While the engine is on, it should always read 13.5 to 14.5 volts. If it goes above or below, you have a problem with the alternator or the wiring to it.
they tested the alternator and voltage regulator as far as I understand
I’ll do it today. At least I can get more data this way.
You most likely have a parasitic drain if your battery is lasting 3 months. Without a charging circuit it would be dead within a few days max. Plus you said it’s charging just fine from the tests.
Remove the negative side battery cable from the negative battery terminal.
Attach an ammeter(this measures amperage) between the negative cable and the negative battery post. Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems “wake up”. After a bit of time they will go back to “sleep”.
If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings)last. Be sure to observe the ammeter after pulling each fuse.
Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners’ manual or service manual to find what circuits are on that fuse.
Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.
Repeat steps 1&2 to test your repair. The ammeter will tell you exact numbers.
I forgot to mention this measurement. I measured 7 mA drain on the battery when the car was off.
Say it was a current drain problem. How can that drop my CCA when the voltage was OK? I would expect to see the battery with an out of spec low voltage. With all 3 batteries the car started just fine, was turned off for less than a day, and then was completely dead or barely able to start the next time I started it.
7 mA is fine. In fact, up to 50 mA is usually considered to be okay. The parasitic drain theory does not fit your situation.
Check to see if there is any AC voltage getting to the battery while the engine is running. There should be no more than .1 volt. If that is ok then I would say there is a bad connection in the power wiring.
I assume you want me to use a standard AC voltmeter. I’ve got a DVM wired to the cigarette lighter so can monitor both DC and AC.
That is correct. Set your DVM to measure AC volts and check the voltage while the engine and alternator are running.
I read a DC voltage between 13.5 and 14.5V except when at idle. The AC was a different story. I’m using a junk Harbor Freight DVM and it it ready 30.1 VAC with the car running and 27 VAC when the car was off. When I unplugged the meter from the car it read 0. I plan to attach my Fluke DVM to the car and repeat that test. If I still see an AC voltage greater than 0.1 I will connect up my scope to see what is really going on.
Using my Fluke 77 DVM I read 0.03V AC with the car running and 0 with it off. So now what?
So its 3 batterys that all show low CCA’s and the batterys were not simply discharged but could not be recharged and the actual sympton was slow cranking.
With repeated failures like this I like to change something in the mix. What I would like you to change is the manufacture of the battery you are using. Perhaps this manufacture is suffering from poor quality control.
I would like you to test both with a conductance meter and a carbon pile. The conductance meter will give a indication of the batterys ability to take a charge.
Foremost change battery manufacture.
At least two of the 3 batteries showed low CCAs before dying. The first one just died and was never tested just before the failure. All of these batteries were under warranty so I just get what they give me. If the batteries had just needed to be charged, I know they would not have given me a new battery. With the second battery they did keep it for a few days to try and charge it up. In the end I just got a new battery.
I do know that the first and third batteries are from Rayovac and the second one was not. I don’t know what equipment was used at AutoZone but do recall that they had some heavy cables to my battery plus a current probe around one of those cables. I had to run the engine up to 3000 RPM for them to do the test. Could they have done one or both of the tests you suggested? The person at AutoZone said all was OK but also warned that their test equipment was not that good.
Cars don’t use A/C voltage, use the DC setting on your meter.
You cant make conclusions based upon what a parts store employee decides to do to make you happy. They will just warranty your battery because it is the path of least resistance leaving you with the conclusion that the battery was bad.
A properly trained mechanic needs to check your electrical system out. What did you pay for the Auto Zone check-out? OH it was free,well you got what you paid for.
True enough. I’ll give up and take it to my mechanic.
Thanks to all for trying to help me.
I believe the trick of reading the AC voltage was to see if there was an open diode in the bridge rectifier. The voltage applied to the battery is not pure DC.
I took my car to my trusted mechanic (he is listed in the trusted section of this web site). I was told that nothing was wrong with the charging system although the battery cables were corroded so I had them replaced. He felt that I just had a series of defective batteries. Not a very satisfying answer. Time will tell if he is right. If this new battery dies in 3 months, I will pay extra for a better battery.