Do you swap/rotate batteries

Picture this, you have say 3 LED torches and as follows:

1. Torch A takes 2xAA
2. Torch B takes 2xAA
3. Torch C also takes 2xAA.

Now all your torches run on Eneloops.

So say after 2 weeks of heavy use all torches batts run flat and you now need to recharge the Eneloops from the three torches.

Once all the Eneloops are fully charged up and ready to be re-used, will you use the batts that were in Torch B into than either Torch A or C, or mix C with A or B with C and A etc, or do you always use the same set of batteries in the same torch no matter what. So say for eg, if you remove the batts from Torch A you will always return those same batts into Torch A etc.

So its not just me thinking like this...

I have been thinking of doing this, useing the same batterys in the same light all the time.

But I really dont think it would make any diffrence? I might be wrong, but it feels weird if it would...

I think I'd keep the pairs of AA paired up.

Switching batteries between lights makes no difference at all.

However, if you use a charger that can determine individual battery capacity (e.g., Maha C9000), you're best off matching batteries with each other as to their tested capacity and keeping those batteries together in whatever device you use them in.
And of course, when a battery drops below expected capacity, it's time to throw it out and replace it.

But swapping pairs of batteries between flashlights?... Naw. Just adds more confusion to keeping track of batteries.

what he said ^
if you Can, its better to keep the same set in the same device, why?

1) if the device is destroying them, no use destroying every battery you own . AKA if you have something that is very hard on the cells, then you would be better to use them in just that device, instead of mixing it with devices that you would get Many more cycles from.

2) keep track of not only the battery but the device by knowing what it was used in. if the device is doing something funkey to the batts, would be good to know which device has the most demand, and therefore use the most robust battery in it.
if it drains cells when off, good to know which device does that.

3) matched cycles and capacity, if you dont have testing, or Waste time piddling with testing the junk, you would prefer that the SERIES cells were all used in similarity, then they will act in similarity and discharge in similarity, reducing the possibility of reverse charge.

4) say some "condition" the light is stored in is causing long term issues, like heat from a car, or moisture, dropping damage, or some other oddity, it might be good (again) to know which condition of storage or use caused a battery to have a short life.

so you would be better off not "rotating" when that would not be as good as keeping TEAMS of batteries together, or just dont worry about nothing because life is to short to get that critical about it.

do I do that? not always, i have way to many batteries, and to many items that they go into, so i Depend on the testing from the charger more. Although, if i just pull cells to charge from a light, and CAN stuff it right back in same said light after charge, i would. generally though i grab another Set, that is already charged instead. Also there are many devices that the batts STAY in to be charged, so they stay a team anyway

so then reverse all that, when rotating means the batteries would get used more, if you have 2 similar lights, one gets used and the other just parks, and neither are damaging the cells, rotating parked cells to a used item, will get the batteries "in use" and therfore cycled. specially if they are still the same TEAM of cells.

I certainly don't rotate batteries between devices on purpose. I purposely try to standardize on just a few battery types so that they can interoperate, but in practice I tend to keep using the same battery with the same light. I don't have any 2 cell lights in regular use at the moment with rechargeables. I prefer 1 cell lights in general.

OK, while we are discussing this aspect of battery use, let me throw out a bit of a curve ball.

In multi cell lights, I will often swap the positions of the cells in the light, about half way through the discharge.

Anyone else do this?

As far as the original question goes, I have a pool of cells less than what is needed to run my lights. When I grab a light, I will grab cells from my working pool of cells and use them in the light. When I am done with the light, I will remove the cells and return them to the working pool.

I tend to use a light for a month or two at a time, then switch to another light.

The exception is my rechargeable lights, like the L7, 8NX, 9AN, and so on. I have around 10 packs for these lights and that is enough for 4 - 5 days of use. Here again, I swap the packs around to whatever light is being used.

Once a year, I do a complete check of all the cells in my working pool and my battery packs. Cells, or packs, that drop below 80% of their initial capacity are recycled.

Tom

SilverFox said:

OK, while we are discussing this aspect of battery use, let me throw out a bit of a curve ball.

In multi cell lights, I will often swap the positions of the cells in the light, about half way through the discharge.

Anyone else do this?

Tom

Click to expand...

I used to, but once my medications got straightened out, I stopped.



Seriously, I would be interested to know the reason you have in mind for doing this?

Hello Zenster,

There have been several threads started about the uneven drain of cells within a multi cell light.

The argument suggests that the cell that is closest to the lamp heats up more than the other cells. The heat reduces the impedance of the cell and it drains faster than the other cells. If this is true (a big IF...), it would be possible to get a little bit longer runtime from your light by swapping the position of the batteries. This assumes that when you use your light, you run it long enough to heat up the batteries.

Tom

While I don't go to the extreme of keeping the same batteries in each flashlight, I do rotate my stock of charged batteries so that the oldest charged battery is being used in the next device that needs it. My NiMh AA batteries just don't go in flashlights; they also are used in my handheld GPS unit and digital camera.

The Theory:
Swapping the position of the 2AA NimH cells when you foresee draining them
during 1 'flashlight episode' half way thru the estimated runtime to
balance the cells discharge thus gaining more photons. -the reason to do this
annoying and tedious process if no spare cells or ability to recharge is easily available.
The Test:
Please chime in with ideas on how to test this without letting unknown factors skew the data...
1. a flashlight that'll get the AA cell closest to the lamp warmer.
2. 2 AA cells tested for equal capacity.
3. Infared thermometer -need measurements data to prove cells at different
temperatures
4. stop watch.
5. May need to simulate the thermal characteristics of a human hand holding
the light. This may add to the temperature rise in the forward cell or
could aid in carrying away heat. Groan! Or maybe not...

6.

SilverFox said:

Hello Zenster,

There have been several threads started about the uneven drain of cells within a multi cell light.

The argument suggests that the cell that is closest to the lamp heats up more than the other cells. The heat reduces the impedance of the cell and it drains faster than the other cells. If this is true (a big IF...), it would be possible to get a little bit longer runtime from your light by swapping the position of the batteries. This assumes that when you use your light, you run it long enough to heat up the batteries.

Tom

Click to expand...

Well, color me "skeptical".
The challenge would be to actually do a clinical test to determine that:
1. The cell nearest the emitter actually does heat up more than the cell further away.
2. If #1 is shown, then it has to be determined if the amount of additional heat actually makes a measureable difference in the useable capacity of that battery compared to the battery further away.

I'm skeptical because even it is shown that there is a difference established in #2, I doubt very much that it would make a practical difference.
If someone does the above testing, I'd be surprised if you would see more than 1% of additional runtime which would be immaterial in the normal course of use.

So at the moment, what we have here is an "urban legend". Now it's time for someone to actually do the testing.

Zenster said:

So at the moment, what we have here is an "urban legend". Now it's time for someone to actually do the testing.

Click to expand...

I have to agree with you that right now it's an urban legend. I have seen numerous examples of 2, 3, and 4 series cell devices drain their cells unevenly...especially NiMh and NiCd without heat being involved (or at least the heat is negligible). I doubt that heat from the lamp head is the cause, but it can't be ruled out. I have seen this effect in Eveready Fluorescent folding lanterns (D cells), stereo boom boxes (D cells), and 3 D cell mag lights, as well as AA cell devices. In the cordless phone business, cell packs with a single dead cell is the most common cause of cordless phones being returned to the manufacturer as defective…all because of one cell that lags behind and does a magical voltage reversal after the second or third discharge cycle. I believe it to be minor differences in internal impedance that are a result of either manufacturing variation or uneven or incomplete charge-discharge cycles and cycle count between the cells in the pack.

Anyhow what I find is, especially, in lanterns is that the brightness all of a sudden rolls off within minutes after running steady for hours. When the cells are measured (NiMh) I typically will find four cells with voltages reading something like 1.15v, 1.15v, 1.16v, and 0.65v. What appears to happen, is that one NiMh cell is pretty much at the end of the charge and that cell rolls off the edge of the discharge curve right at 1.0 volt and that voltage just avalanches straight down. If its not caught soon, it goes to zero, then the remaining 3 cells will literally drive a negative voltage on that cell. I have on several occasions found 4 cells with two or three still with a healthy charge and reading 1.22 volts and one cell reading negative (-) 0.2 volts or something like that.

I think its clearly a case of minor mismatched impedance. Somehow this minor difference is amplified to a distinctly large voltage difference by the time the batteries are 2/3 or more depleted.

Anyway it would be interesting to get a precise test of why or how this happens. Perhaps someone can set up a jig with 3 cells in series, at the same time, bring out a wire as a test node between the cells in a series, then measure the voltage across the cells as the entire series pack is discharged. As far as current, the current flow should be theoretically the same from one end of the cell series to the other, since what goes in must come out in a true circuit. My bet is that even a slight difference in internal cell impedance translates to a growing voltage differential as the pack depletes.

Anyhow, that's my 2 cents and excuse me I've rambled too much.

I dont know how serious you guys are about really doing all this stuff. I would agree that it might be a good idea to shift places of two batterys in a row if the risk of one of them going bad was a real threat.

I think that I am willing to take that risk and just let everything be, If something brakes Im hoping that I have the funds to replace it if it was something I really liked and use. Im that kind of person that could be admitted to a loony house if I was doing stuff like this..
Im trying to focus on more important stuff now, I put way to much time in this hobby as it is...

Hi there,

I have a light (actually more than one) that takes three AAA cells, and
i use rechargables. The problem is that when you go to the store you
can only buy either two or four cells in a pack, not just three.
What i end up doing is rotating which cells i use in the light as they get
discharged so that i end up using all four cells over a long period of time.

For example, first i start out using cells 1,2,3, then the next time i use
cells 1,2,4, then the next time i use 1,3,4, then finally 2,3,4. By doing
this, after four uses i have used each cell only three times, thus using
all four cells evenly over time.

Here's a chart showing each use:

cycle1: 1 2 3
cycle2: 1 2 4
cycle3: 1 3 4
cycle4: 2 3 4

and note that if you count the times each cell is used it will total 3 for
each cell over these four recharge cycles. After the fourth cycle i
start over at 1,2,3.

I think we on this planet should get our priorities straight and first tackle the very serious problem of what Dihydrogen Monoxide is doing to people all over the world. Then we can address the less important issue of how to stack batteries in a flashlight.
http://www.poetv.com/video.php?vid=13045

I think Darkpower nailed the battery issue with this:
"I think its clearly a case of minor mismatched impedance. Somehow this minor difference is amplified to a distinctly large voltage difference by the time the batteries are 2/3 or more depleted."

Even with tight manufacturing tolerances, batteries are, after all, a basic mix of chemicals that cannot be perfectly matched.
Put a group of two or more batteries together, and no two will deplete in exactly the same way all the way to dead.
All that's going on is that people experience a symptom, and then jump to a false conclusion as to the symptom's cause.

Hello Zenster,

Before we totally chuck this into the realm of "urban legend" let me add that I have actually done a little testing on this.

I have a Mag85 with a 9 cell battery holder. I am using Titanium Pow Power 1800 mAh cells in it. I have a matched set of cells based on mid point voltage and capacity that I am using.

When I do a 10 minute burn with the light, and then pull the battery pack and discharge the cells the rest of the way down, I find the cells closest to the lamp have less capacity left than the cells furthest away. However, if I discharge the pack outside of the light, the cells remain in balance with each other.

My cells are balanced on capacity to about 1% of each other. When I am discharging in the light, they end up at around 5 - 6% of each other.

Keep in mind that I have only done a couple of checks on this, and there are a lot of variables involved. You have also brought up the practicality of this, and you do have a point there. It takes some time to unload, reposition, and re-load the battery holder. Also, while I don't think there would be a significant increase in runtime, if you were measuring the light output with a meter, you may be able to see it.

At any rate, I find it interesting that batteries get out of balance, even when a matched set is used.

Now, to get back on topic... The Mag85 is another light that I don't rotate or swap batteries in. I have my matched set and they are assigned to that light, and only that light. In general, with lights that are the most demanding from the batteries you may want to consider coming up with a matched set of batteries to use, but with lights that less demanding, you don't need to go to all the bother with matching a set of cells for use with the light.

Tom

SilverFox said:

At any rate, I find it interesting that batteries get out of balance, even when a matched set is used.

Tom

Click to expand...

I think that pretty much says it all right there.

While interesting, I don't think it's surprising though, because we're dealing with chemistry.
When the chemical soup is put together into a battery, what happens after that, while reasonably predictable, is essentially an uncontrolled reaction between those chemicals. There are lot's of variables that allow no two batteries to work exactly the same so the chemicals have to play things out without any "control" at all.

I know that you know that we're dealing with some pretty small variances here, so God luv' 'ya if you can find the time to do a proper study of it to a point where the theory could be proven.
But even if proven, we all know that the results wouldn't result in any real (practical) difference in runtimes, so I don't think anyone should lose any sleep over it.

But then, who am I to talk... I used to rotate the tires on my bicycle when I was a kid for no other reason than that I saw my dad do it to his car.

Zenster, please bear in mind that this:

SilverFox said:

I have actually done a little testing on this.

Click to expand...

is probably as great an under-statement as you are ever likely to read here on CPF. SilverFox is THE expert in this field.

SilverFox said:

Hello Zenster,

There have been several threads started about the uneven drain of cells within a multi cell light.

The argument suggests that the cell that is closest to the lamp heats up more than the other cells. The heat reduces the impedance of the cell and it drains faster than the other cells. If this is true (a big IF...), it would be possible to get a little bit longer runtime from your light by swapping the position of the batteries. This assumes that when you use your light, you run it long enough to heat up the batteries.

Tom

Click to expand...

Tom, I wish I was meticulous enough to number/label every cell, and always know what position, and in what light they came from....but alas I have too many cells, too many sizes, too many chemistries, too many lights to keep track of them this way. At least I finally started marking with sharpie on side when I received batteries, and when last conditioned. I have a hard enough time keeping track of which bulb in which Mag since the WA all look similar.

If this is a real finding (vs. spurious cell degradation/defects), I think doing a periodic conditioning charge (.1C x 15hrs) would be an easier way (read: "more manageable") to resolve it.