Don't Store 18650's Fully Charged

[Stevo57]

Being new to this, I made the mistake of storing fully charged 18650 cells that I've salvaged from used laptop batteries. Here are the results from the before and after for 316 cells that I had tested using a Litokala Engineer 500, then stored for between 6 mo and 9 mo, at a full state of charge (4.2v nominal).

I totally get that the Litokala tester is not laboratory grade, and that you can run five tests and get five different answers, but it's what I have and I think the results speak for themselves. The majority of the salvaged cells lost some capacity. About 5% lost over 25% capacity. A few were "heaters" to the point I pulled them and called them 100% loss. One cell ended up at 0v, so was a complete loss. Some cells actually showed an increase in capacity on the second test.

I haven't seen anybody produce any real data on this, and while not "scientific grade" data, it's worth showing. First chart is the total population of the test. The second chart is with anything greater than 10% loss pulled from the population. The histogram shows the bucket. The median change in capacity was -0.7%. The Average change in capacity was -0.6%.

So, don't store your 18650's at full SOC!



I've built a few batteries now that work great, and am setting up a solar system. Will show that later. Right now, just enjoying how well they work on my ebike.

My process now is: Salvage cells, keeping the good ones. I do charge up the cells with more than 1.0v, even though folks say these are "iffy". That's probably true.
I test them twice, then store for around four weeks at full charge. Any that drop by more than 0.1v get pulled as "self-dischargers". Then I discharge the remaining cells to about 3.65v using a resistor bank. These are the cells that go into storage until I need them.

When ready to use, I check for self-dischargers again, and those get pulled and sent to recycle.

So, let the trolling begin from all the anti-18650 folks out there. I'm having a lot of fun with these.

Also building a 160AH LiFePo 24V set-up for my camper. I'm using prismatics and its very similar to the one Will has made a video about.

Enjoy, and happy to answer any questions about 18650 usage. I've learned a lot over the past year.

Cheers

 

[DisabledVet]

If you are storing them long-term, you definitely want to store them at 50% charge.

 

[erik.calco]

Being new to this, I made the mistake of storing fully charged 18650 cells that I've salvaged from used laptop batteries. Here are the results from the before and after for 316 cells that I had tested using a Litokala Engineer 500, then stored for between 6 mo and 9 mo, at a full state of charge (4.2v nominal).

I totally get that the Litokala tester is not laboratory grade, and that you can run five tests and get five different answers, but it's what I have and I think the results speak for themselves. The majority of the salvaged cells lost some capacity. About 5% lost over 25% capacity. A few were "heaters" to the point I pulled them and called them 100% loss. One cell ended up at 0v, so was a complete loss. Some cells actually showed an increase in capacity on the second test.

I haven't seen anybody produce any real data on this, and while not "scientific grade" data, it's worth showing. First chart is the total population of the test. The second chart is with anything greater than 10% loss pulled from the population. The histogram shows the bucket. The median change in capacity was -0.7%. The Average change in capacity was -0.6%.

So, don't store your 18650's at full SOC!

View attachment 1726View attachment 1727View attachment 1728

I've built a few batteries now that work great, and am setting up a solar system. Will show that later. Right now, just enjoying how well they work on my ebike.

My process now is: Salvage cells, keeping the good ones. I do charge up the cells with more than 1.0v, even though folks say these are "iffy". That's probably true.
I test them twice, then store for around four weeks at full charge. Any that drop by more than 0.1v get pulled as "self-dischargers". Then I discharge the remaining cells to about 3.65v using a resistor bank. These are the cells that go into storage until I need them.

When ready to use, I check for self-dischargers again, and those get pulled and sent to recycle.

So, let the trolling begin from all the anti-18650 folks out there. I'm having a lot of fun with these.

Also building a 160AH LiFePo 24V set-up for my camper. I'm using prismatics and its very similar to the one Will has made a video about.

Enjoy, and happy to answer any questions about 18650 usage. I've learned a lot over the past year.

Cheers

You mention storing for 4 weeks as a process. But was that the length of time you it took to damage the cells you threw out? Or is this your new test process for used cells?

It's also hard to separate issues related to the cells being old and used vs the impact of storing fully charged (let's say near 4.2V). I am also using the same charger to charge and test my 18650s. I fully tested and charged some a few months ago, and they have sat since. I can retest some. They are all new.

 

[Stevo57]

You mention storing for 4 weeks as a process. But was that the length of time you it took to damage the cells you threw out? Or is this your new test process for used cells?

It's also hard to separate issues related to the cells being old and used vs the impact of storing fully charged (let's say near 4.2V). I am also using the same charger to charge and test my 18650s. I fully tested and charged some a few months ago, and they have sat since. I can retest some. They are all new.

Sorry about the delay in responding. Been traveling. The ones in the graph were stored fully charged for between 6 and 9 months. I agree with you that it is hard to know whether or not the changes are due to that or just what happens with old cells. I've been harvesting more cells and ran into some old Samsungs and LGs from laptop batteries that I estimate to be close to 10 years old. They are in fine shape with capacities north of 2500 mah. I think it's just down to individual cells and when dealing with second life batteries you are going to get a lot of inconsistencies. Hence the need for good protective circuitry in your DIY designs.

 

[SolarRat]

Last year I bought my nephew a drone and 8 battery packs (3.7v LiPo pouch cells) to play with while visiting. On his last day here something happened and the drone flew up up and away, never to be seen again. I tossed the batteries in a drawer, fully charged, and forgot about them. Yesterday I came across them and noticed all 8 were swollen to twice their size and dead!

I've done storage tests in the past with 18650's and they all lost much more capacity when stored at 100% charge for a year than the ones stored at lower SOCs. At 3.7v they lost practically nothing (a few actually gained a bit). But even storing them at 4.1-4.15v was much better than at 4.2v.

I cringe when everyone here charges their big lithium banks to 100%. They'd last a lot longer at 85-95%...

 

[erik.calco]

Last year I bought my nephew a drone and 8 battery packs (3.7v LiPo pouch cells) to play with while visiting. On his last day here something happened and the drone flew up up and away, never to be seen again. I tossed the batteries in a drawer, fully charged, and forgot about them. Yesterday I came across them and noticed all 8 were swollen to twice their size and dead!

I've done storage tests in the past with 18650's and they all lost much more capacity when stored at 100% charge for a year than the ones stored at lower SOCs. At 3.7v they lost practically nothing (a few actually gained a bit). But even storing them at 4.1-4.15v was much better than at 4.2v.

I cringe when everyone here charges their big lithium banks to 100%. They'd last a lot longer at 85-95%...

I think I'll charge my cell phones with 18650s to reduce their SoC. The only problem with that is I'd like for them to double as UPS.

 

[SolarRat]

...The only problem with that is I'd like for them to double as UPS.

I think this is the reason most UPS manufacturers still use LA's...they like to be kept fully charged and ready at all times.

The 18650s that I cycle daily get fully charged to 4.2v, so do my flashlight batteries that I use often (although I really should reduce their charge). The cells I use in radios, emergency lighting and occasional use stuff like metal detectors get charged to 4.1v. The ones I don't have in my "normal rotation" get charged to only about 3.7-3.8v automatically by my balance charger set to "store" and they hold that charge for years. If we are expecting a hurricane I charge them all up ahead of time in case I'll need them.

On a related note, my 2 year old iPhone 8+'s battery lost most of its capacity in just the two years, and I barely use it. I wonder if there is a setting or app that makes it only charge to 80% like I have on my laptop? Gotta be an app for that...

 

[erik.calco]

Not sure what's in my 2013 Chromebook, but I keep it fully charged and plugged in and got 3 hours of Netflix on Wifi outside last summer. I was amazed. When it dies, I'll open it up.

 

[John Frum]

I think this is the reason most UPS manufacturers still use LA's...they like to be kept fully charged and ready at all times.

I've been fiddling with lithium ion based ups.
I charge the 3s pack to 12.3 volts and intend to just leave the charger on.
The inverter draws ~3 watts at idle so that is also trying to draw down the pack.

If anyone has a better idea how to deal lithium ion batteries in the UPS usage model I'm all ears.

 

[John Frum]

I guess I could make a "drinking bird" feedback control.
Turn the charger on at 11.2 volts and off at 12.2 maybe.

 

[DThames]

There may not be any science behind this but when I salvage 18650 cells, I will charge, discharge, charge, and then let them set for a number of weeks. I will then look for cells that still have full charge voltage on them, considering them to be stable. From these I will build my packs. Those that bleed off voltage, I use for junk battery packs where the capacity or holding of charge is not as important.

 

[offgriddle]

Being new to this, I made the mistake of storing fully charged 18650 cells that I've salvaged from used laptop batteries. Here are the results from the before and after for 316 cells that I had tested using a Litokala Engineer 500, then stored for between 6 mo and 9 mo, at a full state of charge (4.2v nominal).

I totally get that the Litokala tester is not laboratory grade, and that you can run five tests and get five different answers, but it's what I have and I think the results speak for themselves. The majority of the salvaged cells lost some capacity. About 5% lost over 25% capacity. A few were "heaters" to the point I pulled them and called them 100% loss. One cell ended up at 0v, so was a complete loss. Some cells actually showed an increase in capacity on the second test.

I haven't seen anybody produce any real data on this, and while not "scientific grade" data, it's worth showing. First chart is the total population of the test. The second chart is with anything greater than 10% loss pulled from the population. The histogram shows the bucket. The median change in capacity was -0.7%. The Average change in capacity was -0.6%.

So, don't store your 18650's at full SOC!

View attachment 1726View attachment 1727View attachment 1728

I've built a few batteries now that work great, and am setting up a solar system. Will show that later. Right now, just enjoying how well they work on my ebike.

My process now is: Salvage cells, keeping the good ones. I do charge up the cells with more than 1.0v, even though folks say these are "iffy". That's probably true.
I test them twice, then store for around four weeks at full charge. Any that drop by more than 0.1v get pulled as "self-dischargers". Then I discharge the remaining cells to about 3.65v using a resistor bank. These are the cells that go into storage until I need them.

When ready to use, I check for self-dischargers again, and those get pulled and sent to recycle.

So, let the trolling begin from all the anti-18650 folks out there. I'm having a lot of fun with these.

Also building a 160AH LiFePo 24V set-up for my camper. I'm using prismatics and its very similar to the one Will has made a video about.

Enjoy, and happy to answer any questions about 18650 usage. I've learned a lot over the past year.

Cheers

Maybe 80/20 is a good general rule of thumb to be gentle on lithiums. What make and model is your ebike, do you have a link to a supplier? Tks.