CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Update- How can i prove this battery is bad

So as I said in another post, I purchased a new battery at AutoZone about 3 months ago. Two weeks ago I had a few slow starts, and thought the battery was no good. However it tested fine and the slow start went away by the time I got to the store. This morning it happened again, very slow start (note I drove the car 2.5 he’s last night ). Went to a meeting and across town and the car barley started. Once again by the time I got to the store the battery tested fine and has been fine all day.

So I think I have a loose connection inside the battery, and driving aroud the vibrations fix it. I did checkedhe cables and everything is tight.

So how do I make the battery fail at the store so I can get a new one??

Please explain what you mean by a “slow start”? Are you saying it cranks slowly, or it takes a long time to start while the starter cranks at regular speed?

is Auto Zone just voltage checking it, or are they load testing it? Have you done a load test on it? If it passes a load test, it is fine. And perhaps you have another issue going on here.

The hardest load on your battery and starting system will be in the morning, especially when it is real cold out.

Beyond a load test, I would be checking for clean and tight battery cables, and morning battery voltage vs evening battery voltage (see if there is a drop over night- if so, you have a draw that is draining your battery overnight, this would cause a weak start, then your alternator charging your battery would fix this by the time you got to Autozone.)

Buy/borrow a multimeter and check voltage before, during and after a slow start. It shouldn’t be below 12 before or after and shouldn’t be much below 10-11 during cranking. After start it should go up to 14ish.
If that checks out, I would look into the starter and cables. With a load clamp you can check the current draw off the battery during cranking. Most of the time a weak starter will test good at autozone if removed from the vehicle.
Also, if the starter is hard to change go to napa or car quest or dealer.

By slow start, I mean slow crank of the motor.

A loose battery post is usually verifiable by manually wobbling the cable.

However, have you had the charging system checked? Your alternator might be the culprit.

It might not be the battery. There may be a parastic current draw on the battery as the vehicle sits. To check for this, remove the negative battery cable as the vehicle sits overnight. Then in the morning reconnect the battery. If the engine turns over normally there’s a current draw on the battery as the vehicle sits.

Tester

Tester gave you the best answer…The problem is most likely in your car, not the battery…

As others have already stated, the trouble is most likely due to a parasitic current draw. Normal draw on a battery while the car is parked and things are in the sleep mode should be around 20 milliamps. If there is over a 50 milliamps draw I would look for a problem. Your issue might involve a draw more than 100 milliamps going from the statements you make about it.

It’s not a draw, and I will tell you why… It can go weeks with out doing it, it all. Also this AM it slow started, I then drove the car 10 min (should have charged the battery), after my meeting (maybe 30 min) it slow started even worse then the first time… Last time it did this I drove the car 2.5 hrs and it did it right after… This is why I think it’s a loose internal connection between battery cells…

A load test is the standard that these stores use. If the battery passes the load test, which means it can deliver the CCA that the battery is rated for, chances are it is not the battery, and they don’t feel obligated to replace it.

The next time you experience a slow start, don’t let the engine start up. Take the battery out and use another car to take it to the store for an immediate load test. It may be a matter of letting the alternator charge up the battery that helps cover the bad condition.

A bad battery case: I had a client come in with a fried alternator in a Ford Explorer. We replaced the alternator, but noticed the new alternator had a strange hum. But, it tested fine, and we sent him on his way. A couple of hours later, he called with the truck not able to start. It jumped fine, but the alternator was fried again. We put a warranty replacement alternator in the truck, and it too had that strange hum. My ammeter told me it was pulling over 95 amps. We shut it all down and checked everything we could. I pulled the battery, and took the client to the store he purchased it from. It checked out voltage-wise, but I had them load test it anyways. The electronic tester they used called for a 30 min charge before it would test it. We waited. Once it ran the load test, the results came back 70% capacity. They replaced it under warranty. Once the new battery was in, the alternator no longer had the hum and the amp draw was a respectable 25-30 amps. My best guess is a bizarre short in the battery that was killing alternators. If that battery had managed to pass the load test, they would not have honored a warranty replacement.

Auto parts stores will do a battery load test usually, for free. That’s one idea. You could have them test the charging system too while you are there.

My guess, tho, this isn’t the battery. You’ve got a connection not making good contact somewhere. The starter motor draws close to 100 amps, so even a 0.01 ohm resistance produces a 1 volt drop , which will noticeably slow down many starter motors. Make sure the battery connections are clean and tight. If that’s not it – unless someone has been messing with the wiring and connections to the starter motor recently-- the next step would be to test the starter selenoid contacts. These contacts failing is a common car problem, and often produce the exact symptom you are reporting. I’m betting this is probably the problem and you’ll need a new starter motor installed. (These days the selenoid contacts are usually part of the starter motor ass’y.)

Here’s a tip for next time you purchase a new battery. When I purchase a new battery, after it is charged up from several days of driving, the next morning, before I start the car, I measure the battery voltage with my DVM with everything off, then I measure the battery voltage with the headlights on bright. That difference, testing the battery with no load, and again with the headlights-on-bright load, is a fairly good measure of the battery condition. The bigger the difference, the worse the battery. That is what a battery load test does .

I hate when you guys are right…lol. Guess what happened when I turned the key to my car this AM … Nothing, nada… Just click… I still though battery and got a jump, So I popped the hood and I could see the alt bumping when I turned the key… So I’m thinking starter is fine… After playing with it for a few min, the click stopped… Did I mention I was in A hotel parking lot 2.5 hrs from home??? Luckily I had a socket set and some wrenches in my truck for just such an emergency…

Any way now I am wondering if I blew a relay or what… So I crawled under it, pulled the splash guard, hit the solenoid and I got my click back… Long story short I pulled the starter on my back in be parking lot and got the car running… Luckily it was a fairly easy starter to get to… I may need to shim it as it does not sound quite right, but I will start a new thread for that…

I would never have called it as the starter sounded great most of the time. The reality is that apparently it has been going bad for a very long time now… Never seen one fail like his before…

Thanks again for the help guys…

It’s not a draw, and I will tell you why… It can go weeks with out doing it, it all.
Also this AM it slow started, I then drove the car 10 min (should have charged the
battery), after my meeting (maybe 30 min) it slow started even worse then the first
time… Last time it did this I drove the car 2.5 hrs and it did it right after…
This is why I think it’s a loose internal connection between battery cells…

It will be tough to find support for your loose internal connection between cells theory.
When I read your above description, I’d be wanting to verify (1): the state of the charging system, and (2): the current draw of your starter when the problem occurs.

If you really want to prove/disprove the battery, the next time it “slow starts”, then immediately pull the battery from the vehicle and get it loaded tested. If it passes the load test, then you need to look for a problem elsewhere.

Joe, my update said it was the starter… I stand corrected on the battery…