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[DerKrawallkeks]

Cyclic aging:

-   Use (charge/discharge) is best with a warm battery (at least 10°C, up to 40°C improves battery life [A p.139]
-   Charge slowly and not to 100% [A p.106]
-   Avoid deep cycles, charge often [A p.139]
-   Regenerative braking actually improves battery life [A p.139]
-   Dynamic loads are not worse than constant loads [A p.140]

Calendar aging:

-   Storage should be done cold (down to 0°C) and at lowest SoC practically possible [A p.71]
Yes, 0% would be the best, anything below 55% is good. Especially if you don’t check often, don’t stay too low, as your BMS drains the battery slowly!
-   The battery actually recovers capacity if it is stored at low SoC! [A p.130]

[DerKrawallkeks]

Hello everybody,

As you know, there’s a lot of conflicting information out there about how to treat your battery.
Many of the instructions are based on reasons like chemistry, usability, comfort, customer-attractiveness. Especially, I strongly disagree with Zeros official instruction to always keep the battery SoC high. It is purely meant to make it easy for the user and avoid warranty-cases, but at the cost of customers wearing out their Zero batteries way quicker than necessary, leading to unnecessary pollution due to toxic waste. I wanted to know the true facts about just the chemistry itself, what is best for the battery cells themselves.

After looking through many many papers on lithium-ion batteries (and especially NMC), I found two very useful ones:

-   A: Ph.D. thesis “Aging of Lithium-Ion batteries in electric vehicles” – Dipl.-Ing. Univ. Peter Keil
-   B: Paper “Calendar Aging of Lithium-Ion batteries” – Journal of the Electrochemical Society

I called these sources A and B.
They both provide great information based on extensive studies, with no manufacturer involved. Both papers have been published very recently (2016 and 2017). Since both papers are very long and might not be understandable without the necessary background, I wanted to condense the most important conclusions as short as possible into practical instructions. The papers contain much more interesting information, so if you want, I recommend reading them.

Aging mechanisms:

1.   Calendar aging: Batteries age over time, no matter if they’re used or not
2.   Cyclic aging: Batteries age when being cycled

Using 1000 full cycles causes similar aging as 15 years calendar life. Storage SoC has similar, slightly higher effect than cycle depth.

It is also interesting to note, that if you always charge your battery to 80% instead of 100%, after a several years someone always charging to 100% will have more range since he stores more energy overall, even though his battery degraded more.
This leads to manufacturers making recommendations like Zero does, to simply always keep it charged.
With that, don't forget that a less degraded battery can be charged to 100% anytime and deliver more range than a battery that has always been charged to 100%.


I might keep modifying this post a little bit.
If you have any questions, feel free to ask and I will try to answer them if I have the knowledge.

best regards

DerKrawallkeks

[TheRan]

I thought Zero recommends storage at 60%, and that when the bike enters storage mode (after being left for 30 days) it will actually discharge to that level if it's above it (and if the charger is plugged in it will charge up to that level once the SoC drops enough, to 30% I think). Also with the SR/F and SR/S they only charge to 80% or so by default and require an override to charge to 100%.

[DerKrawallkeks]

Hey, thanks! That's true, for long term storage zero recommends below 60%. In the diagram I posted, there's a region at 60-70% above which the degradation is much higher. That's the area of the central graphite peak (in another diagram called the differential voltage spectrum). Doesn't matter what that is, it makes sense to stay clear of this area for obvious reasons. The problem is, the central graphite peak can shift around during battery life, so I'd maybe recommend staying below 55%, but Zero probaly knows what they're doing.

My conclusions for storage are for general storage, not just long term. Long term storage is usually done in winter, when battery degradation is low anyway due to the cold, so overall, storage degradation happens much more during riding season, even though the bike is not in permanent storage.

This is mostly meant so you can draw your own conclusions for what you want/can do.

[MVetter]

Are you aware of the actual, per cell, voltage of a Zero Farasis cell when deemed 'full'?

[DerKrawallkeks]

Hey

according to the datasheet, Farasis cells designed to have a maximum voltage of 4,15V-4,2V.

In the Zero, they're only charged to 4,15V, which is a good measure to improve cycle life.
It does help, but there's a lot to be gained by not charging the battery all the way, if you're after battery life.

[MVetter]

4.157

The point being that people often look at studies like this without realizing that Zero already sort of caps the charge to 80%, instead of the full 4.2vdc.

[DerKrawallkeks]

Hey,

4,15V is much higher than 80% SoC on a NMC battery, when 4,2V is considered fully charged.



But it does not really matter what the SoC is, because the voltage is what degrades the cell. It's good they only go to 4,15V

[Crissa]

That might explain why Zeros don't always cut out regen at 100%...

But never, ever store your Zero under 30%.  That results in a dead battery very quickly.

-Crissa

[JaimeC]

Even in this forum we've seen at least one person whose bike was stored at less than 20% and it never took a charge again...  That was supposedly addressed in the most recent firmware updates but it was definitely a wake-up call...

[Zelidar]

Thank you DerKrawallkeks, that was quite an informative post. I especially enjoyed reading some details in the A reference. I hope you don't mind me bringing links to these valuable documents in this thread. None of them are behind paywalls.

A: Ph.D. thesis “Aging of Lithium-Ion batteries in electric vehicles” – Dipl.-Ing. Univ. Peter Keil
https://mediatum.ub.tum.de/doc/1355829/file.pdf

B: Paper “Calendar Aging of Lithium-Ion batteries” – Journal of the Electrochemical Society
https://www.researchgate.net/publication/304994376_Calendar_Aging_of_Lithium-Ion_Batteries_I_Impact_of_the_Graphite_Anode_on_Capacity_Fade/link/577f8ff208ae69ab8823ff4c/download

I look back at 19'000 km driven on a SR/F and what bothered me most with this technology is the significant loss of power (torque) as the SoC decreases. This, alone, would be for me a reason not to drive below 60%.

[MVetter]

I look back at 19'000 km driven on a SR/F and what bothered me most with this technology is the significant loss of power (torque) as the SoC decreases. This, alone, would be for me a reason not to drive below 60%.

That's really a byproduct of how the inverter is designed and programmed. In order to maintain the kW output the amps consumed has to go up as voltage drops. Ride a LiveWire down to very low in the pack and it still gives full power. I've never experienced what it does on any other electric motorcycle.

[TheRan]

The Harley is drawing less than half the current (300A versus 700A) so I guess more consistent performance is another advantage of using a higher voltage. For Zero to achieve the same they'd need to cut the power to SR or maybe even S levels (at that point you're not gaining anything, just giving up power at the higher SoC) or put the SR/F/S controller (and probably a few other bits) in the lower power bikes.

[MVetter]

The Energicas run even higher voltage than the LiveWire, and the Rinehart inverter is a beast and a half, but the LiveWire still outperforms anything I've seen at low charge. Like Folgers, it's good to the last drop.

[Zelidar]

Ride a LiveWire down to very low in the pack and it still gives full power. I've never experienced what it does on any other electric motorcycle.

I never rode one but, now that you mentioned it, I do remember a reviewer mentioning what you wrote.

Funny how at the beginning, when I could test drive a demo SR/F for a couple of days, I thought I would probably not even need a Sport mode. In fact, the first few days I even remained in Eco mode but nowadays I have everything set a 100% and only use the Rain mode when caught in a bad storm.

Anyway, I suppose that getting a decreasing power from a diminishing SoC will in turn increase the overall battery longevity, or so I hope. As can be deduced from the comment of TheRan, one way forward around this limitation would be to increase the battery voltage above 100 V; so no firmware update will ever change that I am afraid.