Charge batteries only to 80% = 4x more cycles?

[helpfulguy]

Is this correct?
If it is, it should be a good way to increase battery life - add 25% energy into your pack and set charger to 80% = profit?

"The battery is rated for 1200 cycles at 0-100% charge until it reaches the 80% of the capacity or 5000 cycles when used 0-80% charge."
Source: http://hybridautocenter.com/HAC4/index.php?option=com_content&view=article&id=72&Itemid=631

Edit: Answer is "YES"

 

[d8veh]

There can be some theoretical advantages and it can also do a lot of harm.

Many types of cell have ingredient X in them that can make them more robust against these things. A big question is what is 80% charge. is it 80% of the maximum you can go on the cells or 80% of what the guy next door does.

If you have a normal balancing BMS that uses bleed resistors to balance, your cells will never get balanced if you charge to 80%.

A normal Ebike battery will last about two years of charging nearly every day, by which time new better batteries will be available anyway, so you'll probably want to change it to get a better one. Look at all the recent developments in frame-tube mounted batteries.Two years ago, they hardly could give 15 amps. Now, they go as high as 40 amps.

 

[joss]

Not fully charging or discharging a lithium cell will definitely extend its life.

Read this entire page at the "Battery University"

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

There are tables on this page to quantify the typical improvement you can expect.

To summarize the way to treat your lithium ion battery well........

1) Never ever allow them to get overheated - period. Heat is the enemy of lithium ion batteries!
2) Never 'hold' the battery at full charge (usually 4.2v) If you want to use the full charge capacity just top up the battery just before you want to use it.
3) Any reduction on the DOD (depth of discharge) will extend the battery life.
4) Avoid ultra fast chargers.

As for not charging a pack up to 100% and therefore not allowing the BMS to balance the individual cells to 4.2Vmax. I would only be concerned if my pack was made from 2nd hand cells of different makes/age. A pack made from the same cells do not tend to drift in my experience. Perhaps a full charge every 10 cycles will allay certain peoples fears?

I'm not aware of any downsides (damage) to cells that are charged to a level below 100% - if I'm missing something perhaps a link to a source of the information can be given?

 

[redilast]

Yes, not using the batteries full capacity will yield more cycles by far.

4.1v = 2x cycle life
4v = 4x cycle life
3.92v = 8x cycle life and used in some military long life batteries

I guess the biggest problem is finding a BMS that supports balancing in this type of situation. I suppose you could always go the hobby charger route as long as your voltage is like in the 24-36v range. Add a BMS just for the low voltage protection but then primarily charge with a hobby charger and the balancing plug. And set the hobby charger to a lower cell cutoff voltage.

 

[Ykick]

Not fully charging or discharging a lithium cell will definitely extend its life.

Read this entire page at the "Battery University"

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

There are tables on this page to quantify the typical improvement you can expect.

To summarize the way to treat your lithium ion battery well........

1) Never ever allow them to get overheated - period. Heat is the enemy of lithium ion batteries!
2) Never 'hold' the battery at full charge (usually 4.2v) If you want to use the full charge capacity just top up the battery just before you want to use it.
3) Any reduction on the DOD (depth of discharge) will extend the battery life.
4) Avoid ultra fast chargers.

As for not charging a pack up to 100% and therefore not allowing the BMS to balance the individual cells to 4.2Vmax. I would only be concerned if my pack was made from 2nd hand cells of different makes/age. A pack made from the same cells do not tend to drift in my experience. Perhaps a full charge every 10 cycles will allay certain peoples fears?

I'm not aware of any downsides (damage) to cells that are charged to a level below 100% - if I'm missing something perhaps a link to a source of the information can be given?

My years of RC Lipo experience pretty much align with your summary #1-3. However, #4 has never really mattered much in my experience.

I’m only talking 10A or 2C charge rates so maybe that’s not “ultra fast” but they sure fill quickly at that rate. And, when I put them on charge immediately following a ride while the bricks are warm, they actually start to cool quite rapidly as soon as the 1-2C charge commences. It’s kinda weird, holding them in my hand it’s almost as if the charge current is helping them cool?

The “only” downside to charging below 100% SOC is if you needed more capacity/range and end up over discharging the cells.

#2 is the most noticeable improvement in longevity I’ve witnessed compared with dozens of RC Lipo bricks I’ve cycled through over 6-7 years.

 

[DAND214]

Redilast said:
4.1v = 2x cycle life
4v = 4x cycle life
3.92v = 8x cycle life and used in some military long life batteries

So you are saying only charge to 4v and discharge to ?
First we say discharge to 3.7 and now only charge to 3.92.
Wow that will get me to the end of the driveway and back.

What cells are rated for 1200 cycles at full charge, LiFePo4?
5000 cycles 80% charge? Wow, new tires, new everything but the batteries.
I do agree with it, but want new ones at most 3 years.
Even 1200 cycles is too long, Got To Have New Stuff, can't wait 6 years. The new stuff will probably be 80% smaller and lighter by then :lol:

Dan

 

[Punx0r]

Don't forget the interplay of calendar life to how long a battery remains usable...

 

[999zip999]

Chemistry is the game changer for charging, discharging and calendar life.

 

[spdas]

#5 should be added: discharging battery more quickly extends the life rather than trickle discharging.

(I got this from a 2 hr tutorial from some professor that specializes in Lithium batteries.) I will try find the youtube as it was very educational and very technical.

francis

 

[joss]

Redilast said:

First we say discharge to 3.7 and now only charge to 3.92.
Wow that will get me to the end of the driveway and back.

Dan

It does look from this that the voltage change will only get to 'down the driveway' but it just demonstrates the very flat part of the discharge curve we are talking about (roughly 20% to 80%). It also demonstrates that using voltage alone is not a good way to measure SOC, particularly when the battery is under load. We need to add in coulomb counting to know "where we are" in terms of energy used.

My e-bike battery cost about US$600 to put together myself (it would have been ~US900 to buy). That is a lot of tyres and other consumables! I also think that the increase in technology benefits is not going to be 80% in 3-6years. If the past 25 years of lithium ion development are taken in account then we can expect about 5% improvement in most metrics/year. However, I respect your right to your desire to to update the technology as it becomes available, its just not that sustainable and damn expensive!

I too hope for a breakthrough technology - we are seeing many promising press releases and very little in the shops. Lithium ion is going to be around for some years to come and indeed may be consolidated as the technology of choice by the Tesla Gigafactory currently under construction. Like it or not this technology leader is entrenching the existing technology! Taking this factor and the upfront costs I'm aiming for a 10yr life for a e-bike battery. I understand that for the RC world the uses and battery life are different, its sometimes difficult in this forum to cover off all user needs/problems/experiences.

Here are a couple of charts to help.....

 

[Hillhater]

Im sure the above data and graphs are relavent to some lithium cells.....but which ones ?
As zip said.....

Chemistry is the game changer for charging, discharging and calendar life.

...so much depends on the actual chemistry.
There is reliable data from NASA showing how charging at 1C will destroy a cells cycle life (Panasonic 18650),....
....but at the same time Tesla are happy to let their packs (Panasonic 18650) charge at 1C+ and still maintain an 8 year warranty ?
Same cell chemistry ?? ...i doubt it for such dramatically different life expectancy.

 

[redilast]

NASA achieved 75,000+ cycles on Sony 18650's with ~30% DOD in 8 years: https://batteryworkshop.msfc.nasa.gov/presentations/27_LEO_Life_Test_ABSL_Sony_18650_GDudley.pdf

-----------------------

Don't forget the interplay of calendar life to how long a battery remains usable...

Honestly I think a quality cell stored properly (cool and low humidity and low SOC 20-40% is ideal) can last a very long time with almost no cell degradation. I've tested several Sanyo 2400mAh 18650's that are over 10 years old. Some were from brand new old stock Fujitsu battery packs, and the others were brand new bulk loose cells. Both delivered darn near perfect original capacity 2380mAh or so, and both had very acceptable internal resistance of ~48 mili ohms @ 1Khz AC. Thats a very similar reading to what I get from brand new fresh Samsung 2600mAh cells. So from what I can tell these decade old cells are probably like 98% as good as fresh cells.

Oh and worth mentioning is some of the Sanyo 2400's from the Fujitsu pack because they sat for 10 years with a BMS which has probably a few micro amps draw, the cells were at around 2.2 volts, yet still zero damage was noticed from capacity degradation or internal resistance vs the 3.7v stored bulk cells of the same Sanyo model.

Now calendar life + hot summer days = definite cell degradation.

 

[friendly1uk]

With 4.1v giving almost the capacity of 4.2v yet lasting twice as long, It's surprising 4.2v was chosen as the standard.

We had a supplier of cheaper boards on the forum this week, claiming their boards balanced whatever the weather. That does bring about other problems but it's a start.
For $20 the programmable smart bms is the only answer I have for lower discharge packs, if you want something you can chuck away in 3 years. This is what I use.

 

[Wheazel]

With 4.1v giving almost the capacity of 4.2v yet lasting twice as long, It's surprising 4.2v was chosen as the standard.

We had a supplier of cheaper boards on the forum this week, claiming their boards balanced whatever the weather. That does bring about other problems but it's a start.
For $20 the programmable smart bms is the only answer I have for lower discharge packs, if you want something you can chuck away in 3 years. This is what I use.

Because the struggle has always been to get batteries with enough capacity. Otherwise they wouldnt be considered at all.
Nowadays we are starting to get the luxury to compromise. I think that 4,1V for example, will be much more common in a few years. At least for applications where cycle life is important.

 

[999zip999]

Chemistry. I use a heavy A123 liefpo4 840 cycles and works great with new 80 amp controller. hoping for many more years of use.

 

[Offroader]

What needs to be experimented more is the optimal range. Is it better to go say 4.1 to 3.8 or 3.7 to 4.0.

What also matters is how much you are using the bike. It may not be worth trying to maximize pack life if you only use the bike a couple of times a week and don't use it in the winter. You'll probably wind up doing a new build and replacing the batteries for better chemistry before you come close to losing a lot of capacity.

I lost only a couple of percent a year on my lipo packs using 4.1 to 3.7. I replaced those with 18650 cells after a few years only lost about 6% capacity.

 

[Hillhater]

^^^+1
With the hugh range of different Li chemistrys and materials used in modern cells, its difficult to believe some of these accepted "facts" about DoD, charge rate, discharge rate, max charge voltage, discharge voltage, temperature, etc , etc,...
.....let alonr the interactive effects of two or more of these combined.
Most users have adopted Lithium because of its higher energy density (weight advantage) so it would seem a waste not to maximise that very benifit by only partially charging or discharging.

 

[joss]

Im sure the above data and graphs are relavent to some lithium cells.....but which ones ?
As zip said.....

Chemistry is the game changer for charging, discharging and calendar life.

...so much depends on the actual chemistry.

Yes, and no, the same general principles will apply. Each change in cathode/anode material and/or electrolyte and or form factor will be done is to improve these performance criteria.

There is reliable data from NASA showing how charging at 1C will destroy a cells cycle life (Panasonic 18650),....

Yes - as I suggested earlier (if in doubt), slow charging is preferred.

.but at the same time Tesla are happy to let their packs (Panasonic 18650) charge at 1C+ and still maintain an 8 year warranty ?
Same cell chemistry ?? ...i doubt it for such dramatically different life expectancy.

As you query, the battery they use has unique chemistry and is not a std Panasonic unit. Apparently the cells which are going to be put into the new Tesla Model 3 are going to be bespoke size also (longer and fatter) than a 18650.

 

[liveforphysics]

Yes, not using the batteries full capacity will yield more cycles by far.

4.1v = 2x cycle life
4v = 4x cycle life
3.92v = 8x cycle life and used in some military long life batteries

Those values seem low, it's not uncommon to see orders of magnitude cyclic improvements through shallow cycling the mid range.

Unlike some types of Nickel based cells systems, it's no 'memory-effect' negative impact, and if you ever want to use the full capacity occasionally for special long distance trips or something, it's available simply by charging to 4.15-4.2v or whatever makes sense for your cells application.

It is true with a crude BMS it could lead to cell imbalances.
It's certainly possible for a BMS to work around this, as many production EV's offer this charging option.

 

[Hillhater]

There is reliable data from NASA showing how charging at 1C will destroy a cells cycle life (Panasonic 18650),....

Yes - as I suggested earlier (if in doubt), slow charging is preferred.

.but at the same time Tesla are happy to let their packs (Panasonic 18650) charge at 1C+ and still maintain an 8 year warranty ?
Same cell chemistry ?? ...i doubt it for such dramatically different life expectancy.

As you query, the battery they use has unique chemistry and is not a std Panasonic unit. Apparently the cells which are going to be put into the new Tesla Model 3 are going to be bespoke size also (longer and fatter) than a 18650.

I dont understand how you can accept that the different chemistry used in the Tesla cells makes such a huge difference in charge level effects, ....yet still think the same general principles apply to all Li cells ??
...Tesla may produce a different cell size, but there is already a Panasonic 20700 cell available.

 

[redilast]

There is reliable data from NASA showing how charging at 1C will destroy a cells cycle life (Panasonic 18650),....

Yes - as I suggested earlier (if in doubt), slow charging is preferred.

.but at the same time Tesla are happy to let their packs (Panasonic 18650) charge at 1C+ and still maintain an 8 year warranty ?
Same cell chemistry ?? ...i doubt it for such dramatically different life expectancy.

As you query, the battery they use has unique chemistry and is not a std Panasonic unit. Apparently the cells which are going to be put into the new Tesla Model 3 are going to be bespoke size also (longer and fatter) than a 18650.

I dont understand how you can accept that the different chemistry used in the Tesla cells makes such a huge difference in charge level effects, ....yet still think the same general principles apply to all Li cells ??
...Tesla may produce a different cell size, but there is already a Panasonic 20700 cell available.

Well I think I pointed this out once before, but the cells that Tesla uses are supposedly similar to the NCR18650BE's which are 10A rated cells and have around 1/2 the internal resistance of the NCR18650A's in the NASA test. So 1C charge rate for the BE's would probably cause roughly the same amount of cell wear/degradation as a 0.5C charge on NCR18650A's. But yes, 1C charge rate on a normal "laptop grade" cell is probably a bad idea. 0.3C to 0.5C is the standard charge current listed on most 18650 laptop grade cells.

 

[Hillhater]

You are obviously generalising without hard facts ,but I think you are simply confirming that different cell chemistry reacts in different ways to various variables ...
....So, when you see statements like "1C charging dramatically shortens cell life",....
Or, " Charge batteries only to 80% = 4x more cycles? ".....
Then you have to be careful where the data is coming from and which actual cell it refers to !
..And im sure you realise that Tesla uses cells from several suppliers ,..LG, Samsung, as well as Panasonic for sure, and i doubt those guys share "secret sauce" recipies !

 

[joss]

You are obviously generalising without hard facts

Can you provide the data for a Lithium battery which actually has a tested longer life (more discharge/charge cycles) when,

a) ....always taken to 100% DOD
b) ......kept at a high temperature
c) .... held at 4.2 volts in storage (where the cell max V is 4.2V)
d) .....has a longer life when fast charged (more than 1C)

There may be exceptions to these rules but in my experience any substantial benefit is traded off against another, IE a high discharge capability battery has a lower overall charge capacity.

The original poster was asking if the life of a particular battery could really have such a dramatically different life when only partially discharged. If the linked info is taken as true then the answer is emphatically yes. The information provided by the subsequent posts may me general in nature but it still holds true. Even the Tesla battery will not like being charged at 5C!

 

[Hillhater]

Can you provide the data for a Lithium battery which actually has a tested longer life (more discharge/charge cycles) when,

a) ....always taken to 100% DOD
b) ......kept at a high temperature
c) .... held at 4.2 volts in storage (where the cell max V is 4.2V)
d) .....has a longer life when fast charged (more than 1C)!

No. And i have never suggested that any of those usage patterns could extend cycle life at all !

....The original poster was asking if the life of a particular battery could really have such a dramatically different life when only partially discharged. ....!

Well, if you read the OP, he was actually asking about the effect on cycle life when only partially CHARGED....!
..there is a difference between the two.!

 

[joss]

only partially CHARGED....!
..there is a difference between the two.!

My apologies and thank you for putting the record straight.