Li-Ion at 3.5v when in storage

dealgrabber2002

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I read that it's best for Li-Ion to be at 3.5-3.6v when leaving in storage for awhile. I think that it a weird thing to do. What happens when I need it during an emergency? I can only use what I have fully charged in my light(s) and have to find a power source to charge the rest of my "resting" 3.5v li-ions...
 

Random Dan

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It is indeed inconvenient, but sadly the battery chemistry doesn't care what you want it to do. That's why I like to keep some CR123 cells around. Of course you can store li-ion at full charge if you don't mind the shorter lifespan.
 

Modernflame

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My solution has been to keep a small number of 18650's fully charged (for me that's ~4.1v), while the rest enjoy a nap in long term storage at ~3.7v. I don't allow any li-on cell to remain at full charge for more than a couple of weeks, so they get cycled through. And yes, I also stock 75-100 CR123 primaries.

You've hit upon at least one reason why NiMH cells are so popular. They are much less needy.
 

Kestrel

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No issue at all here; similar to MF above, I keep my oldest pair of 18650's fully charged, and my newer sets at 60% charge.

60% of 3100-3400 mAh is still a substantial amount of reserve capacity - not too far from the 2200 mAh's we used to have & enjoy.

Am not planning on lighting up our entire city block in an emergency anyhow.
 
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parametrek

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I keep all of mine fully charged. Yeah it might take a year off of the lifespan but li-ion tech moves fast enough that I don't mind buying amazing new cells. I do feel a little bad about wasting money like this just for convenience. But I consider it part of the price of "preparedness" insurance. If the alternative involves stockpiling 100 CR123A then I'm pretty sure I'm coming out ahead.
 

iamlucky13

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I keep all of mine fully charged. Yeah it might take a year off of the lifespan but li-ion tech moves fast enough that I don't mind buying amazing new cells. I do feel a little bad about wasting money like this just for convenience. But I consider it part of the price of "preparedness" insurance. If the alternative involves stockpiling 100 CR123A then I'm pretty sure I'm coming out ahead.

The test data I've seen suggests full charge storage could nearly halve the shelf-life - eg, 5 years to 70% initial capacity instead 8-10 years.

But really, the cost isn't that bad - $5-10 every 5 years for convenience, multiplied by how many batteries? How does that really compare to your other convenience decisions, like eating out when on errands or day trips, versus bringing food from home?

My strategy is mixed. I charge my li-ion batteries all the way up when they go into a light. My plan for spare batteries is to rotate them through - eg, use a battery until it's half drained or so, then charge a battery that is in storage and swap it in.

Ahead of trips or bad weather that might cause a power outage, I fully charge the batteries I want ready, then if they're not needed at that time, just use them in my regular rotation.

Also, if these are just stored batteries for emergency preparedness, look at it this way:

You either need a certain number of batteries stored fully charged to meet your preparation goal, or you need twice as many batteries half charged, but the batteries have as much as twice as long of shelf life. Long term, you get similar total cost when factoring in replacements.
 
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parametrek

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Gauss163, are you thinking of continuously trickle charging a li-ion? That could reduce lifespan by 80%-90% but that isn't what we're talking about.

How does that really compare to your other convenience decisions, like eating out when on errands or day trips, versus bringing food from home?

iamlucky13, It compares very poorly. I like to cook and will go to great lengths to save a nickle :)

In practice my battery handling is identical to yours. Fully charged batteries in lights. But when you have less batteries than lights then all of your batteries are fully charged.
 

Gauss163

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Gauss163, are you thinking of continuously trickle charging a li-ion? That could reduce lifespan by 80%-90% but that isn't what we're talking about.

Trickle charging would be even worse. What precisely do you mean when you say that you "keep them fully charged"? What is their average voltage while in storage?
 

tatasal

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Oh my, this full-charge' versus storage-charge debate is the most ironic thing in this hobby of having a "light in a flash".

..and to avoid this irony, better stay with niMh!
 

WalkIntoTheLight

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You could charge up to 4.2v, then put them in the refrigerator. That would be almost as easy on the cells as charging them up to 4.0v or 4.1v and keeping them at room temperature. Of course, there's the issue of making sure they don't dew up when you take them out of the refrigerator, so it's probably not worth the hassle.

I fully-charge cells (4.2v) for the ones I use on my bicycle, and ones I use for outside walks. Basically, all my Zebralights. I don't want to have to change batteries in the dark, except for when I have to. Most of my other lights (used around the house or seldom used) get charged to 4.1v. I also keep a lot of cells in storage at 3.75v. I could use the partially-charged cell in an emergency, but I'd probably just use Eneloops in that case (which I store fully-charged).

IMO, there's no point in buying a 3500mAh cell if you're only going to charge it up to 2000mAh when you use it. If you want to extend the life of your cells, 4.1v is a good compromise, which gives about a 90% charge.
 

flatline

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I charge all mine to 4.1v. If it shortens the life span, so be it. I'll replace the cells sooner than otherwise. I can live with that.

--flatline
 

Random Dan

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[...]
IMO, there's no point in buying a 3500mAh cell if you're only going to charge it up to 2000mAh when you use it. If you want to extend the life of your cells, 4.1v is a good compromise, which gives about a 90% charge.
I don't think anyone here suggested doing that. We're talking about storage at half charge and if the power goes out and you can't fully charge before use at least you still have some capacity.
 

dealgrabber2002

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Oh my, this full-charge' versus storage-charge debate is the most ironic thing in this hobby of having a "light in a flash".

..and to avoid this irony, better stay with niMh!

I didn't mean to open up a debate. I thought it was weird that this battery chemistry needs to stored at 3.6v, unlike nimh.

Like, hey, don't top off your emergency generator. Just keep it at 50%. If SHTF, you have at least something to use... but it keeps your generator last longer. While using the 50%, you can now go look for more fuels during an emergency. :thumbsup:
 
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WalkIntoTheLight

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I don't think anyone here suggested doing that. We're talking about storage at half charge and if the power goes out and you can't fully charge before use at least you still have some capacity.

I suppose it depends on what one considers "storage". To me, it means I likely won't be using that battery for a year or more. In that case, storing at 50% (3.75v) makes a lot of sense.

Charging to 4.1v is for "I don't use this light much, or I probably won't use it for a few weeks." I get about 90% capacity, but it's much easier on the cells. For me, a good compromise.

Charging to 4.2v is for "I use this light a lot, or I need maximum run-time when I use it". I mainly just do this for my Zebralights (and their spares when cycling). I figure if I pay $100 for a light with a great boost-driver for long run-times, I want to actually get those run-times.

In the end, it's probably not necessary to coddle your batteries. I have 10-year old laptop cells that were almost always kept fully-charged, and they still have about 75% of their original capacity. IR isn't great, but laptop cells never were high-drain.

I'm suspicious of the often-quoted claim that a fully-charged cell kept at room temperature will lose 20% capacity per year. Maybe it does that the first year, and then much more slowly after that? Or maybe it's a claim that's only valid for older technology?
 

Gauss163

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[...] I have 10-year old laptop cells that were almost always kept fully-charged, and they still have about 75% of their original capacity. IR isn't great, but laptop cells never were high-drain

I highly doubt they still have 75% life left if they were kept fully charged most of their life. You'd be lucky to still have 75% even in the best possible conditions. Most laptops of that vintage were lucky to get 1 year life when kept fully charged, e.g. Dell forums were flooded with complaints about laptop batteries dying around the 1 year mark even when they were little used (this led to a class-action lawsuit). Nowadays one can do much better because most laptops now have battery saver software that doesn't fully charge them (and also due to cooler running cpus, gpus, etc).
 
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Gauss163

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[...] I'm suspicious of the often-quoted claim that a fully-charged cell kept at room temperature will lose 20% capacity per year. Maybe it does that the first year, and then much more slowly after that? Or maybe it's a claim that's only valid for older technology?

Keep in mind that the industry standard definition of "end of life" is the point when the cell degrades to 80% of nominal capacity. Most studies don't consider what happens after that point.

20% degradation in one year can certainly occur in poorly managed cells, e.g. that's exactly what happened in said Dell laptops (whose batteries were kept close to fully charged by the laptop and often at elevated temperatures - both of which greatly accelerate degradation).
 
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night.hoodie

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I read that it's best for Li-Ion to be at 3.5-3.6v when leaving in storage for awhile

Since no one has stuck their neck out, I'll do it. That figure is wrong and depending on storage time between charges and usage, you are risking permanently destroying the cells, property damage, and injury. No matter what charge you leave your Li-ion, there is going to be a steady self-discharge. At 3.6V, a Li-ion cell is effectively left with no capacity, no wiggle room for storage time, and could easily slip below 2.5V over time. If it does, and depending on how long it remains below 2.5V, when placed back on a charger, you are risking catastrophic failure in the form of an explosion, and fire.

If not cycled repeatedly within about 2 weeks, store your Li-ion cells between 3.8V and 3.9V (about half-capacity). This gives plenty of room for self-discharge in storage, and reduces the charge time if you pull them from storage.

I am only arrogantly claiming this as fact to sacrifice myself and my notions to more knowledgeable and experienced CPF member dissent regarding this storage voltage.
 
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