Shelflife on an unopened/unused 18650

vlaint

Newly Enlightened
Joined
Dec 6, 2018
Messages
10
I'm planning to buy 10 pieces of Soshine 3400mah since that is what their minimum order is. ilumn,dx,ebay,fasttect don't ship to Philippines sadly and soshine is probably the only bang for buck 18650 I can get. I'd like to know if they go bad since I'm only planning to use about 4 maybe and that's rarely and maybe just sell the others if I can. I wonder if unused/unopened 18650 go bad, I have searched the net but it says it depends on how much you're using it, storage charge or replace after 1 year or 500 cycles etc. I wonder since sellers can't probably recharge or check the batteries since they're in their packaging prior to selling. What do they if for long periods of time no one is buying their batteries to maintain it?
 

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello Vlaint,

Welcome to CPF.

Batteries are a perishable item, so you understand they don't last forever.

Here is what I do. Adjust it to fit your needs and style.

Upon first receiving the batteries I number them, charge them and test them to see what condition they are in. When I charge them to 4.2 volts, are they still at 4.2 volts 1 hour later and also 24 hours later. I then check how optimistic their labeled capacity is. If they state 3400 mAh and test to 3200 mAh that isn't too bad.

This information is documented for future reference.

I pick the ones I plan to use and then do a little over a half discharge on the others. Li-Ion chemistry stores good at about 50% and perhaps a little bit better at 40% charge. You can slow the chemical degradation process down a little by wrapping them against humidity and storing them in the refrigerator. I don't think it is good to store in the freezer. Be sure to let them come up to room temperature before unwrapping when you decide to use them.

Once a year I redo the charge/discharge test and update my reference sheet.

Understand that 500 years from now they will most likely be used up from charge/discharge cycles... :)

Tom
 

kjmccarx

Newly Enlightened
Joined
May 25, 2014
Messages
3
Once a year I redo the charge/discharge test and update my reference sheet.

Do you keep a log of all your data? I'd be interested to know what the average loss of capacity is per year? I'm amusing it will probably be a sort of curve. If you have the data and want me to run a least square fit I'd be happy to!
 

WalkIntoTheLight

Flashlight Enthusiast
Joined
Jun 18, 2014
Messages
3,967
Location
Canada
Yeah, I store extra cells in a sealed bag in the refrigerator. Charged to 3.7v or slightly higher. 3.8v if they're protected cells, since the protection strip adds to self-discharge. Check them every year or two, to make sure they're holding voltage, and recharge to 3.7v if necessary. They shouldn't require much of a recharge, a few minutes on the charger at most. Warm them up in their sealed bags before removing, so you don't cause condensation and don't recharge when cold.

Stored that way, they should last 10+ years. You will lose some capacity, though probably not much. Maybe 10%-20% over that time, though I'd bet on the lower end of that range. The bigger effect will be from increased internal resistance. So, high-drain cells will probably become mid-drain cells after that much time.

This all assumes the cell is high quality to begin with. I'm not sure what Soshine uses for their re-wraps. Probably something like a Panasonic, so it should be fine.
 

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello Kjmccarx,

Welcome to CPF.

Due to circumstances beyond my control, my data on this is private.

I am currently running tests on some cells from 2007. Let me see if I can generalize something on that when I finish the tests...

Tom
 

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello Kjmccarx,

These cells were manufactured in 2006 and I started testing them in 2007. They are quality cells by well known manufacturers and intended for laptop battery packs. The are "optimistically" labeled as 2400 mAh.

My test is designed to study room temperature storage degradation.

The testing involved charging to 4.20 volts at 1000 mA, letting them rest for an hour, then discharging at 1000 mA to 2.50 volts which was specified on the manufacturers specification sheet. Storage involved charging the cells at 1000 mA for one hour, then store on a shelf. Resting voltage during storage was roughly 3.8 volts. The frequency of observations was once per year.

The two brands I was testing yesterday started out at about 95% of labeled capacity for one and 96% for the other. Resting voltage after charging was 4.19 and 4.20 volts. Resting voltage after discharge was above 3.4 volts.

Yesterday both brands ended up with a resting voltage after charging of 4.18 volts. One brand has dropped to 93% of initial capacity and the other brand has dropped to 96% of the initial capacity. Resting voltage after discharge has dropped to 3.3 volts.

As you can see these cells have degraded during the last 13 years of storage...

Tom
 

vlaint

Newly Enlightened
Joined
Dec 6, 2018
Messages
10
Sorry I thought no one was replying since I thought it would show up in the notifications lol.
Hello Vlaint,

Welcome to CPF.

Batteries are a perishable item, so you understand they don't last forever.

Here is what I do. Adjust it to fit your needs and style.

Upon first receiving the batteries I number them, charge them and test them to see what condition they are in. When I charge them to 4.2 volts, are they still at 4.2 volts 1 hour later and also 24 hours later. I then check how optimistic their labeled capacity is. If they state 3400 mAh and test to 3200 mAh that isn't too bad.

This information is documented for future reference.

I pick the ones I plan to use and then do a little over a half discharge on the others. Li-Ion chemistry stores good at about 50% and perhaps a little bit better at 40% charge. You can slow the chemical degradation process down a little by wrapping them against humidity and storing them in the refrigerator. I don't think it is good to store in the freezer. Be sure to let them come up to room temperature before unwrapping when you decide to use them.

Once a year I redo the charge/discharge test and update my reference sheet.

Understand that 500 years from now they will most likely be used up from charge/discharge cycles... :)

Tom

Hi SilverFox. Thanks for the welcome and also for tips, I will certainly make this as a reference once I get my first 18650 light and batteries. How do manufacturers test them though while inside their packaging(not the batteries wrap)? I assume the manufacturers of 18650s unpack them out of their packaging after a certain time if not bought? Just asking since I plan on selling some.

Yeah, I store extra cells in a sealed bag in the refrigerator. Charged to 3.7v or slightly higher. 3.8v if they're protected cells, since the protection strip adds to self-discharge. Check them every year or two, to make sure they're holding voltage, and recharge to 3.7v if necessary. They shouldn't require much of a recharge, a few minutes on the charger at most. Warm them up in their sealed bags before removing, so you don't cause condensation and don't recharge when cold.

Stored that way, they should last 10+ years. You will lose some capacity, though probably not much. Maybe 10%-20% over that time, though I'd bet on the lower end of that range. The bigger effect will be from increased internal resistance. So, high-drain cells will probably become mid-drain cells after that much time.

This all assumes the cell is high quality to begin with. I'm not sure what Soshine uses for their re-wraps. Probably something like a Panasonic, so it should be fine.

Thanks for the info WalkIntoTheLight. I'd like to try the refrigerator method but I'm afraid it will condense lol. I have tried before not with batteries though. When I took the zip lock out it condensed after a while.
I've read the soshines use panasonic cells and read some good feedback on them.
 

WalkIntoTheLight

Flashlight Enthusiast
Joined
Jun 18, 2014
Messages
3,967
Location
Canada
Seems to confirm that storage at proper voltage is fairly kind to lithium-ion cells, at least for capacity. It would be interesting to know how the internal resistance has changed over the past 12 years. Or even what it is now, compared to what the spec sheet says.
 

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello Vlaint,

Most of the batteries from manufacturers are never tested. They pull a few from each batch to check and if no issues are uncovered the rest are assumed to be good.

Tom
 

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello WalkIntoTheLight,

I did not track internal resistance. I did look in on the discharge after about an hour and checked the voltage under load. New it was at around 3.75 volts. This time it had dropped to around 3.70 volts.

Tom
 

WalkIntoTheLight

Flashlight Enthusiast
Joined
Jun 18, 2014
Messages
3,967
Location
Canada
I did not track internal resistance. I did look in on the discharge after about an hour and checked the voltage under load. New it was at around 3.75 volts. This time it had dropped to around 3.70 volts.

3.75v under a 1 amp load after an hour is pretty good. Closest match I could fine on the 18650 comparison site is the Samsung 26F cell. But it doesn't really matter, the other cells have similar voltage differences, just at different drain points.

Anyway, it looks like a 1 amp load drops the voltage by about 0.1v, compared to rest. At least, as best as I can extrapolate. A 0.1v drop on a 1 amp load would be 100mR of resistance, but that's for the whole system not just the battery.

Since you're not seeing much loss in capacity, let's assume the voltage drop after 12 years is up to 0.15v. Now we're up to 150mR of resistance, which 50mR is the increase in battery internal resistance.

I don't know what the system part of the resistance is. Maybe 50mR? It's a guess. But, that would imply a doubling of internal cell resistance over the 12 years of aging.

If the system contributes less to the total resistance, then the results are better.

Meh. Certainly they're not good for high-drain stuff, but it's still acceptable for a lot of lights IMO.
 

vlaint

Newly Enlightened
Joined
Dec 6, 2018
Messages
10
Hello Vlaint,

Most of the batteries from manufacturers are never tested. They pull a few from each batch to check and if no issues are uncovered the rest are assumed to be good.

Tom
Makes sense I guess since they're made in batches. If the voltage drops after 24 hours is the battery considered defective?
 

WalkIntoTheLight

Flashlight Enthusiast
Joined
Jun 18, 2014
Messages
3,967
Location
Canada
Makes sense I guess since they're made in batches. If the voltage drops after 24 hours is the battery considered defective?

At full voltage, it's normal for the resting voltage of cells to continue to drop after 24 hours, but it should be very slowly. A millivolt or two for a few more days, then it should be less than 1 millivolt per day. By the time the voltage gets down to about 4.15v, it should be very stable.

If it's dropping something like 5 millivolts per day (after the first day or two), then the cell is bad.

It might drop 20 millivolts during the first 24 hours, and that is normal. Most of that will be in the first hour or two.
 

vlaint

Newly Enlightened
Joined
Dec 6, 2018
Messages
10
At full voltage, it's normal for the resting voltage of cells to continue to drop after 24 hours, but it should be very slowly. A millivolt or two for a few more days, then it should be less than 1 millivolt per day. By the time the voltage gets down to about 4.15v, it should be very stable.

If it's dropping something like 5 millivolts per day (after the first day or two), then the cell is bad.

It might drop 20 millivolts during the first 24 hours, and that is normal. Most of that will be in the first hour or two.
Alright. Good to know. Thank you for that
 
Top