# So what is the "life span" of Li-ion batteries?



## stumblemumble (Mar 31, 2006)

Seems my Dinotte batteries have lost capacity, I don't have any numbers so it may be in my head. I believe they're 2-3 years old now, used very regularly, and I've followed the rules well: Not left on the charger, not stored for long periods, run mostly on high etc.
Is 2 years about when a drop in capacity begins to show? How long till it's substantial?


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## znomit (Dec 27, 2007)

I think 50% over three years is expected.


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## stumblemumble (Mar 31, 2006)

znomit said:


> I think 50% over three years is expected.


Looks so. Did some digging (I know). http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
Appears capacity drops steadily from first use. Some interesting stuff in there.


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## stumblemumble (Mar 31, 2006)

One interesting fact from the aforementioned link: 
Looks like the best scenario for extending life is storage with 40 percent charge at freezing temperature, which gives a 2 percent capacity loss per year. 
Compare that to storing at full charge and room temp causing a 20 percent capacity loss per year!


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## rschultz101 (Oct 5, 2009)

that is only for the capacity for that particular charge.
it is not for the overall usable capacity after X amount of cycles.
---
here is some rambling on my parts:
for a laptop on daily usage, and daily charge, found that after 2 years,
the usable capacity, to be 1/2 plus, lets say about 60% +/- 10% .
that would be about 700 cycles plus.
regular li-ion cells, usually rated at 300 cycles , ~75% average retaining capacity,
rated to their charge spec.
- the chargers used on bike lights might not be inline with the spec charging of the cells,
for optimal retaining,
- the cells used in bike lights, might not be as high of quality
- the bike light , in most cases, will drain the battery past the optimal usage point

in normal seasonal usage, 2-3 month , 2x week, I'd say 8 years
in cold weather usage worse.
in cold weather, my rule of thumb, to have 2x plus the actual capacity you using.
---
other notes:
- always carry a backup
- if you run down the battery empty, ever, 
basically , you need a bigger battery.



stumblemumble said:


> One interesting fact from the aforementioned link:
> Looks like the best scenario for extending life is storage with 40 percent charge at freezing temperature, which gives a 2 percent capacity loss per year.
> Compare that to storing at full charge and room temp causing a 20 percent capacity loss per year!


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## Cat-man-do (May 16, 2004)

stumblemumble said:


> One interesting fact from the aforementioned link:
> Looks like the best scenario for extending life is storage with 40 percent charge at freezing temperature, which gives a 2 percent capacity loss per year.
> Compare that to storing at full charge and room temp causing a 20 percent capacity loss per year!


Looks like I stand corrected. I previous thought Li-ion storage was not recommended at freezing temperature ( 0'C ) I do know that if you store at very low temps that is best to let the battery warm to room temp before using or charging.

It seems there are many factors having to do with Li-ion cell life. I find it interesting that Battery University (BU) stressed the importance of both storage temperature, state of charge during storage and depth of discharge (DoD) as key elements having an important effect upon cell life. That helps explain why some of my batteries seem to last long while others maybe a couple years. Another key element that often get missed is the previous shelf life of the battery you buy before it becomes yours. BU touched upon this as well. Who really knows just how long those cells you bought sat on a shelf somewhere and under what conditions they were stored? :skep:

Cells that I use in packs ( multi-cell batteries ) tend to age slower. I see that as a direct effect of DoD. As an example: I use a 4Series set-up to power my triple XP-G. Rarely have I ever taken the pack to the *50% discharge level ( * note: my lamp has an led state of charge indicator ). That being the case, those cells will likely last much longer than the one's I use for my torches. Generally speaking, those cells get a much more deeper discharge.

I too have a set of Dinotte (4 cell ) batteries. They might be three years old by now. I haven't used them for a real long time. When I get a chance I'm going to charge up a battery and run it to half charge to judge the capacity. If it runs about 1.5hrs before getting the first warning flash they should be usable. If that is the case I will then stick them in the fridge for safe keeping.

Alas, all of this is somewhat bad news for people living in desert areas. If you use your light/battery in conditons where it is over 86 degrees F. ...your battery is going to age faster then others who live and use theirs in cooler climates.


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## GEOMAN (May 30, 2006)

This is all great info guys, here is the spec sheet from Panasonic for the cells we are using in the GeoManGear 4.5Ah battery packs and the same ones that Open-Light Systems uses in their 4.5Ah packs. The diagram in the bottom right gives you an idea of the diminishing capacity as cycles increase. Bear in mind the previous comments in this thread with regard to all the other variables, but I thought this might be handy. We have this same info on our site

http://www.panasonic.com/industrial/includes/pdf/Panasonic_LiIon_CGR18650CG.pdf


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## stumblemumble (Mar 31, 2006)

GEOMAN said:


> This is all great info guys, here is the spec sheet from Panasonic for the cells we are using in the GeoManGear 4.5Ah battery packs and the same ones that Open-Light Systems uses in their 4.5Ah packs. The diagram in the bottom right gives you an idea of the diminishing capacity as cycles increase. Bear in mind the previous comments in this thread with regard to all the other variables, but I thought this might be handy. We have this same info on our site
> 
> http://www.panasonic.com/industrial/includes/pdf/Panasonic_LiIon_CGR18650CG.pdf


Nice charts, as you say though they do represent perfect world conditions (I have seen the light! :skep: ). Geoman, what do you think is the usual "time on a shelf" for a battery cell between born on date and into the hands of the consumer? Not speaking for the companies you distribute per se, just in general. A year?


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## GEOMAN (May 30, 2006)

Sorry, we really don't have any data on that, Tier 1 cell manufacturers mark each cell individually though which can help identify any cells that are dated, being aware of the battery manufacturers supply chain is vital.



stumblemumble said:


> Nice charts, as you say though they do represent perfect world conditions (I have seen the light! :skep: ). Geoman, what do you think is the usual "time on a shelf" for a battery cell between born on date and into the hands of the consumer? Not speaking for the companies you distribute per se, just in general. A year?


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## Cat-man-do (May 16, 2004)

GEOMAN said:


> This is all great info guys, here is the spec sheet from Panasonic for the cells we are using in the GeoManGear 4.5Ah battery packs and the same ones that Open-Light Systems uses in their 4.5Ah packs. *The diagram in the bottom right gives you an idea of the diminishing capacity as cycles increase. Bear in mind the previous comments in this thread with regard to all the other variables, but I thought this might be handy.* We have this same info on our site
> 
> http://www.panasonic.com/industrial/includes/pdf/Panasonic_LiIon_CGR18650CG.pdf


Yes, indeed. Looking at the chart it is not too impressive. Keep in mind two things, Starting capacity on this cell is about 2200mAh. ( There are cells that have a higher capacity ). Also, when doing a cycle test the cells are usually taken to the point of the safest/lowest discharge the cell can handle. I think most people won't do that every time they use their lights. _The chart that Battery University provided showed that when the Depth of Discharge was cut in half the cycle life tripled._ That's good news for people like me that tend to run lower power levels most of the time. BU suggested that someone concerned about battery life might also consider using a larger capacity battery. In a nut shell, if you had a MagicShine with a four cell battery, using a MS with a 6 cell battery would likely result in a longer ( usable ) battery life ( * as it would effect two main elements of the battery life equation, lower DoD and more starting capacity ). Food for thought. :idea:


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## Turveyd (Sep 30, 2007)

I've got a stack of 18650's, well 13 in use currently, I use and discharge them a lot most of them are going to be 2 - 3 years old, I've not stored them in any way proper generally fully charged and ready to go should the mood take me and I've not noticed any run time drop off at all.

Over discharge, has likely cost me 3 - 4 batterys over the time, go to far and they just won't come back.


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## GEOMAN (May 30, 2006)

Very true Cat, we are finding many of our customers are opting to choose the higher capacity 4-cell 5.8Ah or 6-cell 8.7Ah packs mainly for this very reason, that in 2 years time with significant use they will still have good burntime.

http://www.panasonic.com/industrial/includes/pdf/ncr18650_datasheet.pdf



Cat-man-do said:


> In a nut shell, if you had a MagicShine with a four cell battery, using a MS with a 6 cell battery would likely result in a longer ( usable ) battery life ( * as it would effect two main elements of the battery life equation, lower DoD and more starting capacity ). Food for thought. :idea:


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## rootmaster (Jun 8, 2009)

After riding 20 years with various lighting system (including the very first NiteRider lights), I would encourage everyone to think of batteries just like you would tires. They are consumables. You use them up a little each time you use them and the longer you have them. 

I think I've spent a couple hundred bucks every year on bike batteries on average, but prices are actually lower now because there are more options. If you like to ride at night, that's just what you need to budget.


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## Turveyd (Sep 30, 2007)

Thats the advantage for Torch's and 18650's I buy 2 - 4 occasionally to keep my stock up at $3 a pop so $6 - $12 occasionally.

My batterys in total 13 of them are worth $39 and if 1 dies only the 1 dies.

My HID 8 pack went that was $130 area to replace, just not that rich these days.


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## Cat-man-do (May 16, 2004)

I started buying single 18650's about 3 years ago when I started using torches. While the capacity has dropped on those first cells I still consider them useful for all around torch use. A year ago I bought a 4 cell holder from LuminousDIY and use that to power my triple xpG.
The cells I use for those I use only for the triple. Hopefully I'll get another year or two out of those but really no big thing @ $6 a cell. 

This year I might actually buy a couple of the more expensive AW 2900mAh cells for torch use, just to see if there is any actual difference. I won't consider it a worthy purchase though unless I see at least 10 min. more run time ( over the best cheap D/X cells ).


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