Battery Question

[willbur]

Greetings-
Got a 9 yr.old Interstate Megatron battery used for about 15k miles (don't drive this car much). Charged it at a high rate until specific gravity was almost 1.300 in each cell with only about a 10 point variation from high to low cell. Open cell voltage is 12.8 to 12.9. These results suggest a great battery.
Just to be sure, took it to AZ to be tested. They told me the battery was no good, despite reading 12.9 volts and fully charged on their instrument. Told me a "cell is shorted". My question is: can a battery indicate fully charged specific gravity readings, with little variation between cells, and a 12.8 voltage and still be considered no good? Or, if a "cell is shorted", how can its specific gravity be almost identical to all the others?

 

[JMJNet]

Yes, it happened to one of mine a few years ago.

The voltage does not matter, as soon as the load tester is applied/turned on, it will show 0 Volt.
Not sure how it happened.

 

[mk378]

Does it start the car?

 

[RedOakRanch]

AZ swore my battery was perfect after a few hard starts then it failed completely, I don't test batteries anymore, when they stumble I get new ones. If it starts your car after the headlights have been on for 10 minutes or so I wouldn't worry about it.

 

[JHZR2]

It can read proper open circuit voltage, but have reduced/no capacity, and/or high impedance.

Impedance is easy to see. You load test it and the conduction voltage under load is telling. Capacity is tougher, but assuming that you really just use the battery for starting, it may not matter so much. The recommendation above about starting after running headlights 10 minutes is as good a test as any. Just charge with a proper charger after that, as analternator is not a good approach.

A shorted cell would show up as a voltage around 10V. You cant really have a shorted cell and a full OCV, unless the short was really high impedance, in which case I'm not sure that they could detect it.

 

[willbur]

Originally Posted By: mk378
Does it start the car?



Easily

 

[Colt45ws]

I think they didnt even test it.

 

[Lubener]

Last year I had a battery with a shorted cell, specific gravity was good and even on all cells except one which didn't move the needle on the tester. Open load voltage was around 12.2 volts which is considered "dead".

 

[Nick1994]

I don't trust those testers. They said my alternator was bad on my Camry when testing with the one they hooked up to my battery. Then I took it into the store and they put it in a machine and it tested as good. Then I took it to another store and they tested it hooked up to the battery and it tested as bad. 10 months later it's still working fine.

But a 9 year old battery should have been replaced a long time ago anyways.

 

[eljefino]

I bought a car with a shorted cell and because the alternator was trying to stay at 14 volts each (working) cell was getting 2.8V instead of 2.2. This made it boil over noticeably. Also when I was idling in traffic with the headlights, wiper, and defroster on everything just slowed way down. IMO you'd notice if you had problems.

 

[901Memphis]

If it passes a carbon pile load test then it's good. If the cell is shorted it will probably drop below 9 volts, If it's good it should hold 10.5v+ with a 15 second load high amp load.

 

[user52165]

Originally Posted By: 901Memphis
If it passes a carbon pile load test then it's good. If the cell is shorted it will probably drop below 9 volts, If it's good it should hold 10.5v+ with a 15 second load high amp load.


+1 This

Most newer testers are not a true load tester which requires a carbon pile.

The old school Sun or Snap On battery/alternator testers are great. Readily available on the used market at good prices.

 

[JMJNet]

If the battery starts the car, I would not worry.
It is about functionality not testing the tester.

You did not state that in the first post????

I have a carbon pile tester from HF and it is more accurate than the one at AZ or any part store to detect short, etc.
Yes, I have a battery case as stated in post #2 and it was bad although voltage was good and it did not start the car.

 

[jim302]

The small hand held conductance testers are designed to provide an estimate of how many cold cranking amps the battery can deliver, along with overall state of health. It is an interesting technology to read about, but it is not perfect.

Since it sounds like the battery holds good voltage and can start the car after sitting and letting the surface charge drain off, I don't see how the battery could have a bad cell. Something else going on in the battery may be confusing the tester. It is, after all, a 9 year old battery. That's rare. Since it sounds like you don't drive the car much, keeping an old battery may not be that big of a deal... especially since it still starts the car. Also, with these testers you are generally supposed to read the temperature of the battery to get an accurate result. Inputting the wrong CCA could also lead to an inaccurate result.

If you want to try another test that, you could find a place that has a carbon pile load tester which puts an actual load on the battery for 10-15 seconds. Since that is a longer time than you normally need to start a modern gas engine, the load test could reveal a problem that you haven't seen yet when starting the car.

 

[willbur]

Thanks to all for your comments and ideas.

I charged this battery very thoroughly and bled off surface charge by letting it rest for several days. Then I took it in to AZ.

I can load test by cranking for 15 seconds; and if voltage stays above 9.6, then all is ok. I must be careful not to overly stress (overheat) a very expensive starter.

I may just install an AGM (less sensitive to sitting unused) and be done with it. Otherwise, using a questionable battery may stress the alternator.

 

[shurguywutt]

https://www.amazon.com/Schumacher-BT-100-Battery-Load-Tester/dp/B000AMBOI0

You need a battery load tester. Tests up to 1000 CCA. This is important for battery testing.

Battery maintenance is another thing. People don't do it anymore. It is important to check the levels in your battery and top off with distilled water. You also have to use a battery tender if you do not drive the car a lot. I trickle charge my daily driver once a month because it is almost 4 years old. A battery that stays fully charged lasts exponentially longer.

 

[willbur]

Thank you Shurguy-

You have used this tester yourself? Does it work as advertised?

Yes, I "water" my batteries religiously and check gravity, voltage, terminals. My batteries last a long, long time. Had one at 13 years and it would have gone longer if the knucklehead I sold the car to did not leave the lights on over night several times, despite the warning chime. This buckles the plates and shorts the cells.

DD Honda battery is also 9 years old and still going strong.

 

[shurguywutt]

Yes wilbur I have this tester. But I paid like 50 bucks for it at a local auto parts store in a pinch. It is pretty good especially for the price. It is basically a huge resistor coil that puts a load on your battery as if you were starting your car. Then the readout tells you what condition your battery is in under load. You can also use it to test your alternator from what I remember.

People also forget to clean their batteries, terminals, and then reconnect and grease them. This helps keep the battery from "ghost draining" by making contact with all the debris that builds up on the battery.

You seem to know about batteries if you have batteries that last that long. I am sure you know that a load test is the only way to truly test your battery.

 

[willbur]

Shurguy-
yes, I know about load testing but was reluctant to buy a tester-more stuff to clutter the garage.

However, for $20 with free shipping from Amazon; it confirmed the voltage and specific gravity readings that battery was good (but at low range). Not bad for a 9 year old battery.

Thanks for the heads up.