Trying to Play Battery Detective...

[IamMatt]

My digicam uses 4 AA's; I have three sets of pretty new Duracell 2500mAh NiMH's. I THINK some of them MAY have gotten overcharged on an older charger. I have no diagnostic tools other than a basic volt/ohm meter.

I have the batteries in three sets of 4 which I rotate in the camera. I have noticed one set seems to last much less time than the others, and I suspect it may have a cell or two that are not up to snuff, possibly from the overcharging.

After getting the "change the batteries" message in the camera after having "set B" in for only a short time, I put them in my Vanson BC-2HU and I noticed that one of the four battery's indicator light turned from red to green much quicker than the other three.

Could that be an indication of that cell being bad in some way, and the cause of that set lasting less time in the camera than the other sets? Or would it mean that that one is good and the other three are bad? Or nothing?

I don't want to buy a lot of testers and stuff to try to sort out 5 or 10 bucks worth of batteries, but if there is an easy way to figure out if some of them are not up to snuff, it would be great.

TIA.

Matt

 

[Power Me Up]

If you don't want to buy any extra testing equipment, you could just run the suspect set down until the camera stops working and then test the terminal voltage on each of the cells in the set. From what you're saying, one of the cells may have a significantly lower voltage than the other cells - that would be the problem cell...

 

[SoundMix]

There has been a lot of discussion about faulty cells. For some reason various cells will not hold a charge properly and discharge way too fast. I also notice that these cells either heat up or terminate erractically. In some chargers they may not want to start charging. I've had this prblem with Energizer 2500 and Sanyo 2700.

If you dropped one of the cells that could also cause the problem.

I now use Eneloop batteries and am retiring all the others as they fade.

You could check the voltage as it comes off the charger and again after it fails to find the faulty cell(s).

 

[IamMatt]

If you don't want to buy any extra testing equipment, you could just run the suspect set down until the camera stops working and then test the terminal voltage on each of the cells in the set. From what you're saying, one of the cells may have a significantly lower voltage than the other cells - that would be the problem cell...

You could check the voltage as it comes off the charger and again after it fails to find the faulty cell(s).

Thanks to both of you; sounds like you are both suggesting something similar.

Do I just test the batteries without being connected to anything (open curcuit)? I just took them off the charger and all 4 measured 1.4 volts.

 

[Power Me Up]

Thanks to both of you; sounds like you are both suggesting something similar.

Do I just test the batteries without being connected to anything (open curcuit)? I just took them off the charger and all 4 measured 1.4 volts.

I wouldn't expect that measuring their open circuit voltage after being charged to tell you much.

It would be best to test them after the set is rejected by the camera.

If you can test the cells individually under some sort of reasonable load, that would give you a much better indication of which cell is faulty. Even if you can't test the cells under load, if one cell is significantly degraded, you'll probably still see some voltage difference when tested open circuit.

 

[LuxLuthor]

Go out and buy the $20 cheap Radio Shack digital voltage tester. You will recover that expense over your lifetime. No other practical answer to these types of questions.

How much was your digicam? And you want to screw around possibly messing it up to save the $20 on a DMM tester that is simple as pie to use? There are times to be frugal. This is not one of those times.

 

[IamMatt]

Go out and buy the $20 cheap Radio Shack digital voltage tester. You will recover that expense over your lifetime. No other practical answer to these types of questions.

Is that because a cheap Radio Shack digital voltage tester has an option to put a load on the batteries and test them?

My cheap Radio Shack analog voltage tester does not have that option, but we have some clocks around that run a single AA where the terminals are accessible when the clocks are running and I could test each battery's voltage while they are in the clocks.

Is that the idea behind testing them under load? Is a clock enough of a load to do whatever it is that it needs to do? I just tested each of them in a clock and they were all about 1.4 volts. I can do the same thing after they are in the camera, or do I need something that puts more of a load on them?

Would the discharge function in my BC-2HU be too much of a load or too quick to do what needs to be done?

 

[LuxLuthor]

Well first you want an actual number of a Digital Volt Meter, not the estimated Analog type. I missed that you even had the analog one. But what we are saying is to see if you have something like a light that can run them down to basically not working, and take a DMM reading.

The problem with using all at the same time in the digicam is that if one is the weak link, they will all stop when that one bad battery gives the bad performance sign in the digicam...and they will all have the same reading.

You need to then individually find a light or something that will run them each down to their end point...such as a light. Then take each out and measure the reading to see if one is significantly worse.

This was the appeal of the Maha C9000 charger that is discussed in this batteries section of the forum. It has the ability to give accurate capacity of AA batteries as well as rejuvenating them.

It's hard to give you a real useful answer since there are so many potential issues that could be affecting these batteries. I can tell you that batteries which I gave up on were brought back to life when I properly cycled and/or conditioned them. This is discussed in that C9000 thread.

 

[bfg9000]

Well first you want an actual number of a Digital Volt Meter, not the estimated Analog type. I missed that you even had the analog one. But what we are saying is to see if you have something like a light that can run them down to basically not working, and take a DMM reading.

The problem with using all at the same time in the digicam is that if one is the weak link, they will all stop when that one bad battery gives the bad performance sign in the digicam...and they will all have the same reading.

If batteries in series behaved this way, then there would be no problem with unprotected lithium ions in series, no? The voltages won't be equalized; the only trick is the reading must be taken immediately after the load is removed.

I have long wondered why there isn't a standard CPF resistor value that people could use to load test a 123A or AA with a DMM, but every time I've brought it up the standard answer has always been to just buy a ZTS tester or a MH-C9000.

In this case, why buy a $20 digital DMM that isn't necessarily any more accurate than an analog one? We don't even care about accuracy here, only precision because we are checking relative values.

My suggestion is to run them in the camera until it shuts off, then mark and replace the one low cell. Run it down with the remaining three cells installed + one new one, then check the three to see if the voltages nearly match. If they do, then you've isolated your one bad cell.

A clock won't provide nearly enough load, but the other way to load test them is to use a 1AA incan light to check the brightness under load by eye. This is a surprisingly sensitive test and the dud cell should be obvious.

 

[Power Me Up]

I'll second everything that bfg9000 said.

One thing that I'd add would be that if you don't have a specific need for a DMM, and you want to spend some money, you're probably better off buying some new eneloops or other low self discharge cells...

 

[LuxLuthor]

I disagree with almost everything that bfg said, but his comments have little to do with the posters issues, so not worth getting sidetracked with all the illogical or unrelated opinions.

Lithium cells in series has nothing to do with this situation. No serious user uses an analog volt meter to get an accurate understanding of a situation like this.

There is no way to know if one, two, three, or four cells are bad, or if the charger has a problem...and bfg & power's suggestions do not help to figure out the issue. If he wanted to just keep buying new batteries as the answer, he would not have made the post he did.

 

[Power Me Up]

I disagree with almost everything that bfg said, but his comments have little to do with the posters issues, so not worth getting sidetracked with all the illogical or unrelated opinions.

I'd still say that his comments have everything to do with the situation...

Lithium cells in series has nothing to do with this situation.

His point was that if you have a set of cells running in series under load and one cell is poor, it's terminal voltage will be lower than the others.

One key point with NiMH is that the voltage will recover after the load is removed, so testing the cells under a reasonable load would help give a better indication of which cell (or cells) is bad.

No serious user uses an analog volt meter to get an accurate understanding of a situation like this.

Other than being easier to use, a DMM won't really help that much over an analog meter - unless it's one which can place a reasonable load on the cell under test.

A clock will certainly not provide enough of a load to give any better indication than a simple open circuit test. The discharge function on the BC-2HU would probably be OK for the purpose, although I don't know exactly what load it would put on the cell...

If you wanted to use an ordinary resistor as a load, a 1.8 ohm, or 2.2 ohm 1 watt resistor would be fine (In my humble opinion) A smaller wattage resistor would be fine for a quick test, but it wouldn't be much of a saving. The actual resistance wouldn't be that critical either - anything between 1 ohm and 3 ohms would probably be fine.

There is no way to know if one, two, three, or four cells are bad, or if the charger has a problem...and bfg & power's suggestions do not help to figure out the issue. If he wanted to just keep buying new batteries as the answer, he would not have made the post he did.

I'm not saying that he should just go out and buy more batteries to fix the problem - I'm saying that buying new batteries is probably a better option than buying a new multimeter - if he wants to spend money at all...

 

[bfg9000]

I disagree with almost everything that bfg said, but his comments have little to do with the posters issues, so not worth getting sidetracked with all the illogical or unrelated opinions.

Lithium cells in series has nothing to do with this situation. No serious user uses an analog volt meter to get an accurate understanding of a situation like this.

There is no way to know if one, two, three, or four cells are bad, or if the charger has a problem...and bfg & power's suggestions do not help to figure out the issue. If he wanted to just keep buying new batteries as the answer, he would not have made the post he did.

You know Lux, we really like you but it is just mind boggling that someone who has been here for nearly two years with thousands of posts, amassed an impressive array of FM lights, and just recently went on a threadcrapping crusade against charging Li-ion in series... still does not seem to understand that series does not balance cells. Parallel does. When drained in series the weakest cell will have the lowest voltage under load, whether Li-ion or NiMH. It's just not dangerous with the NiMH.

I don't believe analog or digital has any bearing on the quality of a meter, but seeing how you don't trust your $20 meter anyway (the very one you recommended IamMatt to buy), why don't you send it to him when you get a new one? We'll be happy to chip in for postage.

I think if you had read the 1st post before recommending he buy equipment, you would have seen that he suspects one particular cell in one set while the other sets work just fine. Logically that should eliminate the charger as a problem.

 

[SilverFox]

Hello Matt,

Let's take a look at this, step by step.

My digicam uses 4 AA's; I have three sets of pretty new Duracell 2500mAh NiMH's. I THINK some of them MAY have gotten overcharged on an older charger. I have no diagnostic tools other than a basic volt/ohm meter.

I have the batteries in three sets of 4 which I rotate in the camera. I have noticed one set seems to last much less time than the others, and I suspect it may have a cell or two that are not up to snuff, possibly from the overcharging.

I think you have diagnosed the problem very well.

There are some "issues" here. When using batteries in a "set" you should not replace just one cell of the set with a new one. This will end up unbalancing the others.

It seems you have several sets. If they are roughly the same age, you may be able to break up one set to act as replacement cells for the other sets when they start showing similar problems.

Looking at it from a single set perspective, when one cell goes bad in a battery pack, it is time to replace all the cells.

After getting the "change the batteries" message in the camera after having "set B" in for only a short time, I put them in my Vanson BC-2HU and I noticed that one of the four battery's indicator light turned from red to green much quicker than the other three.

Could that be an indication of that cell being bad in some way, and the cause of that set lasting less time in the camera than the other sets? Or would it mean that that one is good and the other three are bad? Or nothing?

You are right on the money here. The cell that goes from red to green first, is the weakest one. In a matched set, all of the cells should go from red to green at roughly the same time.

The load provided by your charger is about 350 mA. That is a reasonable load for diagnostic assessment.

We are making some assumptions here. We are assuming that the BC-2HU is being used to charge the cells, and there is little slot to slot difference in the charger. Also, we are assuming that the charger is discharging to the same point for each of the slots.

I think those are reasonably safe assumptions.

I don't want to buy a lot of testers and stuff to try to sort out 5 or 10 bucks worth of batteries, but if there is an easy way to figure out if some of them are not up to snuff, it would be great.

TIA.

Matt

I think that if you are willing to watch a discharge cycle, you have all the equipment you need. Run your batteries through your camera then transfer the batteries to the BC-2HU for discharge. They should end the discharge at roughly the same time. If one of them ends early, it is the weak cell.

The big question is, Why is the cell going bad?

There have been a lot of problems with 2500 mAh cells developing high self discharge rates. On the other hand, perhaps you have run through your 500 cycles and the cell is simply worn out.

To test for high self discharge rates you need to charge the set up and let it sit for a week. Open circuit voltage is pretty accurate in determining which cells are self discharge faster than the others. I have a set of 2500 cells that is measuring in the range of 1.296 - 1.300 after around a month.

I would recommend that you match up all four sets that you are using. Charge your batteries up and run them in your camera. Discharge them on the BC-2HU. If would be best to add one important piece of test equipment for these tests - a timer. This will allow you to compare the different sets to each other. In general, matching attempts to get the cells within 2% of each other.

As a point of interest you can figure out how much capacity is left in your cells after the camera shuts off. Capacity is given in Amp Hours or Milli Amp Hours. The discharge rate for the BC-2HU is 350 mA, and with your timer you can obtain the number of minutes to complete the discharge.

Let's say it takes 30 minutes to discharge your cells after they come out of the camera. That is 0.5 hours, and at a discharge rate of 350 mA, it works out to 175 mAh of capacity left in the cell (or 0.175 Amp Hours).

Expensive test equipment automates this process and gives more accurate information, but I think you can do just fine with what you have.

Tom

 

[IamMatt]

As a point of interest you can figure out how much capacity is left in your cells after the camera shuts off. Capacity is given in Amp Hours or Milli Amp Hours. The discharge rate for the BC-2HU is 350 mA, and with your timer you can obtain the number of minutes to complete the discharge.

Let's say it takes 30 minutes to discharge your cells after they come out of the camera. That is 0.5 hours, and at a discharge rate of 350 mA, it works out to 175 mAh of capacity left in the cell (or 0.175 Amp Hours).

First off, more thanks for all for your information.

Just rereading this old info raised a question. If a battery is not lasting "as long as it should," is that measured by how many mAh's is has when it is fully charged? That is, would a poorly-performing AA NiMH rated at 2500 mAh only have, say 2000 or 1500 or 1000 mAh when fully charged? And could that be measured by fully charging the battery, then starting the discharge function on the BC-2HU and timing how long it takes to fully discharge (using the same 350 mA rate to figure out how many mAh's it discharged?)

Assuming I have the time and patience to do this over the possible 7-hours it might take, would this be the best way to accurately measure the capacity of each battery?

 

[SilverFox]

Hello Matt,

Yes,

Yes,

and yes.

Tom

 

[qwertyydude]

I find after fully charging the batteries and then fully discharging the same batteries as a set and then measuring their maximum current capability, basically shorting out the battery with the current setting for your multimeter for a short period of time is a good way to weed out bad cells that may still have normal looking open circuit voltage. They can fool you. I look for batteries that can't sustain at least 2 amps on a dead short on your multimeter. Most nimh will do at least 6 amps.