# Minimum safe voltage for 18650?



## Tachead (Feb 15, 2016)

How low do you discharge your 18650's before charging guys? I rotate cells so I usually swap them out at between 3.65-3.75V so the ones that are sitting there are in a safe state for storage. How low can you go before it will lower your cycle life, capacity, and/or hurt the cell though? I know with my 3.7V lipo cells, you should never discharge below 3.75 volts. Thanks:thumbsup:


----------



## NoNotAgain (Feb 15, 2016)

Tachead said:


> How low do you discharge your 18650's before charging guys? I rotate cells so I usually swap them out at between 3.65-3.75V so the ones that are sitting there are in a safe state for storage. How low can you go before it will lower your cycle life, capacity, and/or hurt the cell though? I know with my 3.7V lipo cells, you should never discharge below 3.75 volts. Thanks:thumbsup:


If you were to look at the protection circuit designs on the market, it appears that 3.0 volts is as far as they will allow you go before the IC shuts things down.

I don't knowingly allow my batteries below 3.3-3.4 volts.

Recently had a pair of batteries in a Nitecore TM06 go wacky and run two them down below 2 volts, to the big scrap can in the sky they went,


----------



## HKJ (Feb 15, 2016)

NoNotAgain said:


> If you were to look at the protection circuit designs on the market, it appears that 3.0 volts is as far as they will allow you go before the IC shuts things down.



What protection do you get that voltage from? The ones I have seen goes lower.


----------



## Tachead (Feb 15, 2016)

Anyone else? HKJ what do you think? What is the minimum safe resting voltage for an 18650 before damage is done(reduced cell life, reduced capacity, exc.)? Thanks:thumbsup:


----------



## MarioJP (Feb 15, 2016)

So let me get this correctly. It only take one time to ruin a good cell if you discharge a 18650 unprotected cell below what the datasheet says?


----------



## HKJ (Feb 16, 2016)

Tachead said:


> Anyone else? HKJ what do you think? What is the minimum safe resting voltage for an 18650 before damage is done(reduced cell life, reduced capacity, exc.)? Thanks:thumbsup:



Looking at the datasheets the minimum voltage is between 2.0 and 3.0 volt, protections usual disables the cell between 2.0 and 2.5 volt.



MarioJP said:


> So let me get this correctly. It only take one time to ruin a good cell if you discharge a 18650 unprotected cell below what the datasheet says?



No, you have to get fairly low to permanently damage the cell. 

I do not have the correct numbers, but I have run cells below rated minimum voltage without damaging them and I have also run cells nearly down to 0 and that have damaged them.


----------



## ven (Feb 16, 2016)

In some of my mods with built in voltage cut off, it tells me at around 3.15v....every time and also a visual symbol or actual figure. 

Other mods stop working at 3.5v

Flashlights I rarely get lower than 3.6-3.8v then top back up. Reasons , turbo may be unavailable or even high depending on the light. I don't want to be left in the dark with a light and only 3.3v left, so a kind of "ready to go again" for next use mind set. Also quicker to top off say at 1a from 3.8v than example of 3.0v ......plus it's a part charge and not a full cycle. 

As long as not going bellow 3v every time , I would say work with what works best for your uses and play safe with a 3.2v rule if taking them down(allows a little amount of error ) Some lights will not function down to 3v , so to go out with 1/4 of a tank could leave you in the ....

Of course some lights tell you by loosing higher modes, others by flashing etc. Would be a bit lame if 5mins into a hike and running cells down....Not saying you would, just an example of running cells down bellow 30% or so. 

I have slight battery OCD , so always aware of where I am at, most of the time can guess the voltages pretty close .:laughing: 

Couple of examples (this is me though ) Home lights, vinh creations then if I take some out and use, I will top back up, be it 3.6v or 3.8v. Lock out ready for next weekend etc

Work lights- these tend to be used sub 200lm, closer to 100lm various times during the day. If I have had short use I will not top cell off . I will use again next day before topping up. Never had a cell go bellow 3.6v. If it's had a few hours use that day, cell will get topped off next morning and swapped for fresh. I don't always carry lots of cells to swap in bigger lights(unless it's use requires it) However in work I have spare single cells so even if I ran it down enough to warn me, it's a few seconds of inconvenience swapping out..........well maybe not as I usually have another 6-8 lights good to go! :laughing:


----------



## Tachead (Feb 17, 2016)

Thanks for the replies guys:thumbsup:


----------



## erict18650 (Feb 17, 2016)

I store mine at 3.7v but I always wondered a few things. I check them monthly but how far should I let them drop before charging them? Also, when charging do you just charge them till 3.7v and store them again if not using. Now what do you guys do to have a light at the ready? Do you always keep some cells at 100% charge?


----------



## cancow (Feb 17, 2016)

So are you guys saying that a 30 day run time is impossible because you would charge your battery after 10% of its usage???


----------



## ChrisGarrett (Feb 17, 2016)

cancow said:


> So are you guys saying that a 30 day run time is impossible because you would charge your battery after 10% of its usage???



If I'm not going to be using certain cells, they get discharged down to 3.6-3.7v, placed in plastic snap cases, then ZipLocked and off to the fridge they go.

I run cells down to 3.4v, 3.5v and even further, just for shits and giggles, so I'm not too worried, but I don't want to kill things prematurely if I don't have to.

Li-ions can be recharged after even a drop to 4.10v, but I don't fret over that too much.

I remember starting out with them and my Xtar WP2 II charger would undercharge a bit and I'd take the cell off and reinsert it to get it up from say 4.17v, to 4.19v just because this is America and bigger is better!

Smarter people than I thought that this might not be a good practice for the cell, so I stopped.

When they get down to that 3.5v-3.6v level, it's probably a good idea to charge them back up.

Now, if you're going to be out 'caving' and your cells are at 3.9v, I'd probably charge them up before I went traipsing off.

Chris


----------



## MarioJP (Feb 18, 2016)

I am confused with the 2 different voltage types. 4.2v-4.35v. I ask this because i realized that my power bank might be for 4.35v cells. Whenever i charge the cells to 4.2v on the charger and put the cells back in the power bank. The power bank reads 75 percent instead of 100. So i thought this could be a fluke. So just to rule things out. I plug the power bank to a usb port. I notice the 100% percent blinking. Waited 5 minutues and still blinking. I pull the cells out to read their voltages. It reads 4.23v. But these cells are rated 4.2v and no more. Yet, the description of the power bank says that it is compatible with any 18650 cells. This is very confusing. I am used to seeing gauges 100% not 75%. Could this compromise safety , let say i decide to go out of town and only method to charge these cells is with the power bank itself??

Thanks lol.


----------



## andrewnewman (Feb 20, 2016)

MarioJP said:


> I am confused with the 2 different voltage types. 4.2v-4.35v. I ask this because i realized that my power bank might be for 4.35v cells. Whenever i charge the cells to 4.2v on the charger and put the cells back in the power bank. The power bank reads 75 percent instead of 100. So i thought this could be a fluke. So just to rule things out. I plug the power bank to a usb port. I notice the 100% percent blinking. Waited 5 minutues and still blinking. I pull the cells out to read their voltages. It reads 4.23v. But these cells are rated 4.2v and no more. Yet, the description of the power bank says that it is compatible with any 18650 cells. This is very confusing. I am used to seeing guages 100% not 75%. Could this compromise safety , let say i decide to go out of town and only method to charge these cells is with the power bank itself??
> 
> Thanks lol.


Could you post the make and model of the power bank? I assume it didn't come with batteries. Some higher capacity 18650s are designed for a maximum charge voltage of 4.30-4.35. Best as I can tell these are safe to charge to 4.20 but will have less capacity than they are rated for. Obviously it isn't safe to charge them above this. If your power bank charges them higher it is not a safe situation. I would consider not using the power bank if you can't get a definitive answer. It's pretty easy to get 4.30-4.35v 18650s these days but I would worry that the power bank might not terminate properly and be unsafe even with the higher voltage rated batteries. The "any 18650" statement is almost certainly not going to be true as LiFPO4 batteries only charge to 3.6V. I would read that claim, rather, as "all typical 18650s" which these days have a maximum charge voltage of 4.20.


----------



## MarioJP (Feb 20, 2016)

andrewnewman said:


> Could you post the make and model of the power bank?.



http://www.amazon.com/gp/product/B00MLTZ3LE/?tag=cpf0b6-20

It has been reviewed and was recommended. The description makes it seems that you can just use any 18650 cell, charge and forget it lol. No issues when discharging though. cuts off around 3 to 3.2v

Unless it has a setting that i am not aware of to switch to 4.2v? Lol.


----------



## andrewnewman (Feb 20, 2016)

MarioJP said:


> http://www.amazon.com/gp/product/B00MLTZ3LE/?tag=cpf0b6-20
> 
> It has been reviewed and was recommended. The description makes it seems that you can just use any 18650 cell, charge and forget it lol. No issues when discharging though. cuts off around 3 to 3.2v
> 
> Unless it has a setting that i am not aware of to switch to 4.2v? Lol.



BLF has a review of this box. The reviewer claims that the charge cutoff is 4.23V (similar to your experiences). This is *basically* ok for most 4.20 LiIon 18650s but obviously on the high side (4.25 might be the cutoff for safety). Probably a touch hard on your batteries but if everything else checks out, you should probably continue to use 4.20V batteries as the 4.35V ones won't yield any advantage capacity-wise.


----------



## MarioJP (Feb 20, 2016)

andrewnewman said:


> BLF has a review of this box. The reviewer claims that the charge cutoff is 4.23V (similar to your experiences). This is *basically* ok for most 4.20 LiIon 18650s but obviously on the high side (4.25 might be the cutoff for safety). Probably a touch hard on your batteries but if everything else checks out, you should probably continue to use 4.20V batteries as the 4.35V ones won't yield any advantage capacity-wise.


Its a start because i was not getting any clear answers. I even contacted the seller. With that said. I'll come back with an update to verify this. I am charging the cells and this time set the termination voltage to 4.23. When i put these cells back in and turn on the power bank it better say 100%. I'll be back with an update lol.

Update: looks like i can finally relax now. It turns out the cells were slightly undercharged than i thought. Exactly terminated at 4.23v. Put the cells back in the power bank and it now reads 100%. Furthermore, no more charging going in to the cells when i plugged the powe bank to a usb port. Finally can put this to rest. I suppose that it's better to be slightly paranoid than to blindly venture into unknown territory and boom when you at least expected i guess lol.

Once again. 

Thank you!


----------

