Question about battery cycles

[DreamCat04]

Hi LTT forum. as you all know, batteries can only sustain a certain amount of cycles. But what does it actually mean when a battery has 1000 cycles on it? (I mean I know that it will have lost quite some capacity by that point) Or more precisely at what capacity will the battery be at when it has reached its specified cycle count?

[Kilrah]

Pretty much impossible to know unless the manufacturer has given specs. 

[mariushm]

21 minutes ago, DreamCat04 said:

Hi LTT forum. as you all know, batteries can only sustain a certain amount of cycles. But what does it actually mean when a battery has 1000 cycles on it? (I mean I know that it will have lost quite some capacity by that point) Or more precisely at what capacity will the battery be at when it has reached its specified cycle count?

It's a rating...  It's sort of like saying  "we guarantee this battery will still have 75% of its original capacity after 1000 discharge - charge cycles and other technical properties are within some percentage of original values"  or something like that. 

 

It's not like there's an internal counter which makes the battery die the instant it's discharged after the 1000 charge, it has to do with internal damage in the battery due to charging the battery at very high currents, due to heat during charging, and other factors. Charging battery at lower currents results in longer life and more recharge cycles.

 

Here's a datasheet example for a regular 18650 battery : ICR18650_4400mAh_3.7V.pdf

 

At page 3, you can see it says it's rated to more than 500 cycles, and it explains how they determine this number : 

 

Discharge to 3.0V @0.2C, then 0.5c CCCV  0.01C charge to 4.2V, rest for 10 min. discharge @ 0.2C to 3.0V and rest for 10
min. Continue the charge/discharge cycles until discharge capacity lower than 70% of rated capacity

 

 

[DreamCat04]

4 hours ago, mariushm said:

It's not like there's an internal counter which makes the battery die the instant it's discharged after the 1000 charge

I knew that this would not happen but thanks for the knowledge :). So it really is just like the best before date on foods where the manufacturer says like "I can guarantee that it will be good until the date written but it might still be good after that date"

[Kilrah]

Not really, because early failures can still happen. 

[mdecima]

2 hours ago, DreamCat04 said:

I knew that this would not happen but thanks for the knowledge :). So it really is just like the best before date on foods where the manufacturer says like "I can guarantee that it will be good until the date written but it might still be good after that date"

There is no standard for that, it depends of the manufacturer,the type of battery, components, etc. and almost none release this info.