Lithium battery longevity

[Otter Spotter]

In all the blurb and utube videos about Lithium batteries and how they will do 3500/4500 full discharges and recharges before they reduce to 80% no where have I seen ‘ what happens if you don’t let it fully discharge to 0% and instead it just goes done to say 40/50% and is fully charged up again‘? Will the battery last indefinitely or will it still reduce down to max power of 80% due to age and if so what age ?

 

[pappajohn]

Fully discharge to zero % is a no-no.....you'll kill it the same as a lead acid.
80% discharge is the limit.

 

[Otter Spotter]

Fully discharge to zero % is a no-no.....you'll kill it the same as a lead acid.
80% discharge is the limit.

Ok but what happens if you never get near 80% discharge ?

 

[Tombola]

They actually like a charge up smaller and more often, and charges are cummulative, and they dont mind being left at 50-60-70% for long periods, and dont require charging to full.
Unlike lead acid that any charge will count as a "charge" in its lifespan,

never getting to 80% is fine

 

[pappajohn]

Nothing I guess....80% is a limit, not a target.

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[paddymcc]

On the Roamer app it shows the number of cycles the battery has undergone. It seems to calculate a full cycle as an accumulation of partial cycles. I reckon I will be long dead before it gets to 4000 cycles.

 

[Raul]

In all the blurb and utube videos about Lithium batteries and how they will do 3500/4500 full discharges and recharges before they reduce to 80% no where have I seen ‘ what happens if you don’t let it fully discharge to 0% and instead it just goes done to say 40/50% and is fully charged up again‘? Will the battery last indefinitely or will it still reduce down to max power of 80% due to age and if so what age ?

I’m not sure where you found 3,5-4K cycles fully discharged and only 20% degradation. Not even high grade EV cells can achieve that. The degradation will be allot more. Maybe 2k full cycles with 20% degradation, and 3,5-4K partial cycles. Rate of discharge is more important than the 20%SOC limit. There’s no such thing, 20%limit, that will kill the cells, but a combination of factors that can accelerate cell degradation. I would be very happy discharging past 10% SOC at 0,05C or below and ambient of 25deC, but will refrain discharging with 0,5C and above at 5degC sub 30% SOC.
Rate of discharge and temperature are more important than the state of charge.

 

[Hoovie]

usually 0% on a Lithium is not actually 0% on the cells as the BMS cuts out.

As far as a 0% reading on a battery goes, you can do this on a Lithium Battery without a problem and it will not damage the battery, but a regular full discharge will impact the charge cycles.
And as far as Lead Batteries are concerned, actually with some (Lead Carbon) you can also take down to 0%. Unlikely you would as the voltage would be too low to be useful but they do NOT get automatically damaged contrary to popular opinion.

I think the folk who advocate limiting the discharge and charge levels on Lithium need to do some maths. Say using a Lithium is a normal way (full charging, pretty well full discharge) will get you 2000 cycles. if you did this level of use 2 times a week, that works out to be around 20 years. If you wanted to make the battery last to say 6000 cycles by stopping charging fully and not discharging below say 20%, you could get 60 years! Very handy for the typical Motorhomer
And remember to get that extra service life, you need to double up the battery count to get the same usable capacity. So extending the battery life will cost twice as much and with no real guarantee you will actually extend the life as you still have things like the cheap electronics in the BMS to factor in. Will they really last 20 years even, let along 30, 40, 50 or even 60?

 

[Raul]

Yep, the bms will be long dead before the cells. That’s why set the system to work above bms limits.

 

[Otter Spotter]

I must have not explained myself properly, in simple terms if a lithium battery only gets discharged say down to 50% each time, will the battery last longer (and by how much?) than one that regularly gets discharged down to 0% to 10% ?
I am asking this as I don’t envision, if I have Lithium that I would let it draw down to 0% to 10% and so I would think the battery should outlive me.

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[Bessy765]

My Transporter batteries are guaranteed for 10 years I think to 80%

 

[Gromett]

I’m not sure where you found 3,5-4K cycles fully discharged and only 20% degradation. Not even high grade EV cells can achieve that. The degradation will be allot more. Maybe 2k full cycles with 20% degradation, and 3,5-4K partial cycles. Rate of discharge is more important than the 20%SOC limit. There’s no such thing, 20%limit, that will kill the cells, but a combination of factors that can accelerate cell degradation. I would be very happy discharging past 10% SOC at 0,05C or below and ambient of 25deC, but will refrain discharging with 0,5C and above at 5degC sub 30% SOC.
Rate of discharge and temperature are more important than the state of charge.

Cells used in EV's tend to be discharged fairly quickly. If you spec your cells so you are only discharging at .5C then you can see greater than 5000 cycles before significant loss of capacity for good quality LiFePO4 batteries. Discharging at only .5C is not practical for an EV hence the batteries will not last as long as in a normal light leisure usage scenario.

I read a research report on this and will try and dig it out later for you.

 

[Gromett]

I will just add, that until recently EV's didn't use LiFePO4 chemistry they used the more volatile but higher energy density chemistries. These do NOT have the lifespan of LiFePO4 chemistry.

 

[Raul]

BYD did cells for Chinese internal consuption market been used on buses. Recycled then sold as B grade all over the world. Lishen does the battery packs for Dacia Spring that’s currently in production in Europe. Early first EV’s attempts had Winston thuntersky good for 3C on EV”s. Not common in Europe at all but elsewhere in the world are still used for EV conversions.
The point I was try to make was that rate of discharge and temperature will dictate significantly the life of cells.
I am aware that production EV’s now uses different chemistry. I have two close mates that uses recycled leaf packs for their house. They come from Norway scrap yards.

 

[Theonlysue]

Fully discharge to zero % is a no-no.....you'll kill it the same as a lead acid.
80% discharge is the limit.

That's the same % as gel batteries.
Is that right?

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