AW 2900 mAH 18650's -- Questions about care and maintenance!

Juanderful

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Hey guys, I've searched online for some answers but only found bits and pieces of information that don't completely answer the questions I have in mind.

So, to be specific, I bought 2x 2900 mAH protected 18650's to use in my new JETBeam PC25 flashlight. One is always in the light, and one is stored in a battery case. So my questions are as follows:

1) How should I store the battery that I am not using? Should I store it in a fully charged state? I've read some people saying that I should store it in a fully-charged state. And other people say that 18650's should be stored after: fully charging it, then discharged a little.

2) As for the battery that's being used in the flashlight, when is the optimal time to charge it? Do I wait until the 18650 is completely drained to recharge it? Or do I recharge it before it is completely drained?

3) I've read in some places that there is something called "memory", and it is best to fully discharge it the first time a 18650 is used.

4) Since the 18650's I bought are "protected", what exactly does that entail? I know roughly that being "protected" means that the pcb prevents the battery from being overcharged/overdischarged. So if it is indeed "protected", doesn't that mean I could fully drain my battery and not worry about damaging the battery? (since the pcb will do its job of "protecting" the 18650 and shut it off accordingly)

If someone could explain these to me, that would be great.
 
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Th232

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1) It should be stored at 40% charge in a cool place. I think 40% was around 3.7 V.

2) Best to charge as often as possible, Li-ions prefer multiple shallow discharges over a single deep discharge.

3) Can't really help you.

4) Protection should be taken as a last resort, many protection circuits cut out at 2.5 V, when damage is already occurring. Think of it like a car's airbag. While you could theoretically use the airbag for protection, it's better to not crash in the first place, and by the time you're using it you've already damaged your car.
 

samgab

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Juanderful

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Thanks for the links!

1) It should be stored at 40% charge in a cool place. I think 40% was around 3.7 V.

2) Best to charge as often as possible, Li-ions prefer multiple shallow discharges over a single deep discharge.

3) Can't really help you.

4) Protection should be taken as a last resort, many protection circuits cut out at 2.5 V, when damage is already occurring. Think of it like a car's airbag. While you could theoretically use the airbag for protection, it's better to not crash in the first place, and by the time you're using it you've already damaged your car.

In the link that samgab provided, it stated this:

2-3-2 Long-term storage characteristics
When batteries are stored over a long period, depending on the battery state and the
storage temperature, in some cases irreversible deterioration may occur and the
battery will fail to hold a charge even after recharging. Deterioration is not observed in
batteries in the discharged state, but the greater the charge in the battery, the more
pronounced the deterioration after storage. Also, the higher the storage temperature,
the greater the deterioration tends to be. For these reasons, lithium ion rechargeable
batteries should be in the discharged state when stored for extended lengths of time,
and it is desirable that they be stored in a low-temperature environment.

So which is right? 40% discharged or completely discharged?
 

45/70

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Hi Juanderful. First, memory, as it is often referred to, is associated only with NiCd cells. NiMh cells can suffer a similar effect, but for different reasons.

Storing Li-Ion cells at a 40% SOC (state of charge) helps to prevent the cell from self discharging during storage, and thus damaging the cell. Li-Ion cells should never be fully discharged, as in zero volts. Depending on the chemistry of the cell there is a minimum voltage where damage will occur if the voltage drops below this point.

There is a chart on this page from Battery University that gives a general idea of how storage conditions affect Li-ion cells. The site also offers much information about not only Li-Ion cells, but other rechargeable cells, as well.

Dave
 

infinus

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Wait a second, let me get this straight, did you buy an extra cell simply to "store" it?

I do similar to you, where I have (for my single cell lights) one cell in the light and one in a battery carrier, however I carry the extra as a spare and I constantly rotate it with the one in the light. So the battery in the carrier is fully charged. Every day or 2 I'll swap it into the light and then charge up the other one and put it in the carrier. This way I always have an extra cell on hand should I need it and it's ready to go.

I think you need to ask yourself..... did you really buy an extra cell simply to store it? Where it will degrade regardless of what charge state you leave it in? Or did you buy it to use it?
 

Juanderful

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I have another question. Given the scenario that I am camping or something, and I forget how much juice is left in my 18650. Would it be detrimental to the 18650 if I accidentally drain the battery completely (i.e. at the point where the pcb cuts off the current), as long as it's not on a regular basis?

Hi Juanderful. First, memory, as it is often referred to, is associated only with NiCd cells. NiMh cells can suffer a similar effect, but for different reasons.

Storing Li-Ion cells at a 40% SOC (state of charge) helps to prevent the cell from self discharging during storage, and thus damaging the cell. Li-Ion cells should never be fully discharged, as in zero volts. Depending on the chemistry of the cell there is a minimum voltage where damage will occur if the voltage drops below this point.

There is a chart on this page from Battery University that gives a general idea of how storage conditions affect Li-ion cells. The site also offers much information about not only Li-Ion cells, but other rechargeable cells, as well.

Dave

Ah okay, thanks for the info!

Wait a second, let me get this straight, did you buy an extra cell simply to "store" it?

I do similar to you, where I have (for my single cell lights) one cell in the light and one in a battery carrier, however I carry the extra as a spare and I constantly rotate it with the one in the light. So the battery in the carrier is fully charged. Every day or 2 I'll swap it into the light and then charge up the other one and put it in the carrier. This way I always have an extra cell on hand should I need it and it's ready to go.

I think you need to ask yourself..... did you really buy an extra cell simply to store it? Where it will degrade regardless of what charge state you leave it in? Or did you buy it to use it?

Yeah, I use my flashlight enough so that my spare battery is swapped out once every week. So I was just wondering if I should precharge my spare battery to max and then store it. Or if I should store my spare in a discharged state, and when I want to swap it out, I charge to max then.

According to most of the people in this thread, I guess I should leave it at ~40% charge when I store it.
 
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samgab

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In the technical handbook, when they talk about "storage", they don't mean for a week or two, they are talking about a year or more.
When they talk about ZERO capacity, as you can see in the charts, they are referring to 3.3V. When they talk about storing at 50% capacity, they are referring to 3.8V.
They don't state NOT to store with full capacity, they just provide charts that demonstrate, that IF one stores a cell with 100% charge for 1 year, that cell will have lost about 80% of its' capacity after 1 year of storage in that state.
If one chooses to store it for a year with 50% capacity, at the end of that year it will have about 95 or so % of it's starting capacity.
And, if one chooses to store it for a year at 3.3V, or "zero capacity", at the end of that year it will still have nearly 100% of its' initial capacity.
(Edit, that is if it is stored at 45 degrees C (VERY HOT) for that whole time. The effect is less pronounced at a regular room temperature of about 22 degrees C.)
They have proved this with testing, and provided graphs to demonstrate the effect.
Having said that, there is no issue with carrying your spare cells around for a week or so with full capacity in them.
I do it, and I know they won't last as long as if I carried them around empty, but what good would that do me? I don't care if my cells only last 2 or 3 years, if the tradeoff is better functional use for me, in the duration of that time.
Basically, do whatever is most convenient for you, the user.
 
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Juanderful

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In the technical handbook, when they talk about "storage", they don't mean for a week or two, they are talking about a year or more.
When they talk about ZERO capacity, as you can see in the charts, they are referring to 3.3V. When they talk about storing at 50% capacity, they are referring to 3.8V.
They don't state NOT to store with full capacity, they just provide charts that demonstrate, that IF one stores a cell with 100% charge for 1 year, that cell will have lost about 80% of its' capacity after 1 year of storage in that state.
If one chooses to store it for a year with 50% capacity, at the end of that year it will have about 95 or so % of it's starting capacity.
And, if one chooses to store it for a year at 3.3V, or "zero capacity", at the end of that year it will still have nearly 100% of its' initial capacity.
(Edit, that is if it is stored at 45 degrees C (VERY HOT) for that whole time. The effect is less pronounced at a regular room temperature of about 22 degrees C.)
They have proved this with testing, and provided graphs to demonstrate the effect.
Having said that, there is no issue with carrying your spare cells around for a week or so with full capacity in them.
I do it, and I know they won't last as long as if I carried them around empty, but what good would that do me? I don't care if my cells only last 2 or 3 years, if the tradeoff is better functional use for me, in the duration of that time.
Basically, do whatever is most convenient for you, the user.

Hm, good points, thanks for the insight :) Sometimes it's easy to get caught up in the technical side of things, while forgetting the practical aspects of them, as I did. I guess I'll just go with the flow and act per circumstance. I just wanted to make sure I wasn't doing anything terribly wrong.
 

infinus

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I agree with samgab completly. That was the point I was trying to make. It would be a pain to always be charging to 40% just for a few days to a week then fully charging. Given your situation, fully charge it and then swap it in after you use the light for a bit! In 2 years buy some new cells (and maybe a new more powerful light!)

:)
 

shadowjk

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Empirically from my own experience, 3 months of storage at <3.3 gives a 10% decline capacity, and quadrupling or worse of internal resistance...
 
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