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[NEW2elec]

Once again I'll take the financial angle.  For the Gen 2 bikes Zero says charge the bike to 100% and unplug it.
Since only Zero and not any battery expert or battery paper author is going to give you a free replacement battery under warranty.
I suggest following their recommendations.

I did that on the original battery yet it failed (less then 80% capacity) so don’t want a reoccurrence.

Do a google search on optimized Li-Ion battery SOC & you come up with many recommendations for 80 max & 30 or 40 min.
Zero doesn't list a recommended running minimum level.

I only need about 30-40% for each leg of my commute. 
Why stress the battery by charging it to 100% & then drain it to sub 30%?

I’m going to plug in on both ends of my commute & limit charge to 75% -+ 5 & try to keep up on cell balance.

And did you get a free replacement battery when you did what Zero recommended? 
I'm adding a second line so you can read between them.     

[ESokoloff]

You're not stressing it by charging to 100% if you're actually going to ride the bike after, just don't store the bike at 100%. I would say you're going to do more damage (still not much) going from 75% to 35-45% with an unbalanced battery.

Define Un-Balance.
The answer is important in this discussion & I don’t know what that # is.
On my last/present charge, SOC=83% Balance=3.5mv (avg) so I’m calling that acceptable. 


I agree that 80/40 is likely to be easier on the battery then 70/30 balanced or not.
Watts is AxV so the lower the SOC (V), the higher the A & that causes heat & perhaps increased stress.
Something caused my 2016 DSR battery to loose much more then the 20% (30-40% I’m guessing) in less then 5yrs that warrant a replacement & I don’t want to repeat that.
I did purchase the bike used (10months/2.8k miles) so I don’t know it’s full history.
I rode several 100+ mile charges early in my ownership so I don’t think the battery was extremely compromised @ time of my purchase. 

It was during the past couple of Winters that I had a sense that the range was taking a hit (reduction).

I strongly feel that SOC/charge termination should be optimized.
Question is were is that sweet spot?

Again my old charge pattern was 100%-20 (or less).

[ESokoloff]

Once again I'll take the financial angle.  For the Gen 2 bikes Zero says charge the bike to 100% and unplug it.
Since only Zero and not any battery expert or battery paper author is going to give you a free replacement battery under warranty.
I suggest following their recommendations.

I did that on the original battery yet it failed (less then 80% capacity) so don’t want a reoccurrence.

Do a google search on optimized Li-Ion battery SOC & you come up with many recommendations for 80 max & 30 or 40 min.
Zero doesn't list a recommended running minimum level.

I only need about 30-40% for each leg of my commute. 
Why stress the battery by charging it to 100% & then drain it to sub 30%?

I’m going to plug in on both ends of my commute & limit charge to 75% -+ 5 & try to keep up on cell balance.

And did you get a free replacement battery when you did what Zero recommended? 
I'm adding a second line so you can read between them.     

Yes I did but I’m not wearing my glasses right now & the coffee has yet to kick in so I’m missing that second line your referencing.
??

[NEW2elec]

I'm saying it's best to get a new battery for free then to go out on your own and maybe get your battery to last 6 years before there is a problem while it was still under warranty.  Those five years do what they say do.  If they change their recommendations then do that.

The basic thought is if the cell unbalance is under 10mV you're fine.
Remember that Zero's stated 100% SOC in not the true battery 100% capacity. No need to worry much about that unless you store the bike at 100% out in the sun when it's very hot.

A < 20% SOC is worse than 100% SOC for any long (few days) period of time.

And last, Li ion just isn't the long term solution.  The cells degrade over time no matter what you do.  I doubt you'd find a healthy (85-95% capacity) battery pack in any 8 year old EV.
 
Will the cells they make today be better and hit that mark in the future?  We'll see.

[TheRan]

You're not stressing it by charging to 100% if you're actually going to ride the bike after, just don't store the bike at 100%. I would say you're going to do more damage (still not much) going from 75% to 35-45% with an unbalanced battery.

Define Un-Balance.
The answer is important in this discussion & I don’t know what that # is.
On my last/present charge, SOC=83% Balance=3.5mv (avg) so I’m calling that acceptable. 


I agree that 80/40 is likely to be easier on the battery then 70/30 balanced or not.
Watts is AxV so the lower the SOC (V), the higher the A & that causes heat & perhaps increased stress.
Something caused my 2016 DSR battery to loose much more then the 20% (30-40% I’m guessing) in less then 5yrs that warrant a replacement & I don’t want to repeat that.
I did purchase the bike used (10months/2.8k miles) so I don’t know it’s full history.
I rode several 100+ mile charges early in my ownership so I don’t think the battery was extremely compromised @ time of my purchase. 

It was during the past couple of Winters that I had a sense that the range was taking a hit (reduction).

I strongly feel that SOC/charge termination should be optimized.
Question is were is that sweet spot?

Again my old charge pattern was 100%-20 (or less).

Cell balance will get worse as the SoC decreases, over time, and under load. The further out of balance the cells are the worse some of them will "wear" compared to others which in turn is going to make the balance even worse in the future. Balancing happens for a reason and it's silly to avoid it just for the sake of not charging the battery to 100% (which it's designed to do).

[ESokoloff]

“ Balancing happens for a reason and it's silly to avoid it just for the sake of not charging the battery to 100% (which it's designed to do).”


3.5 MV average isn’t balanced?

[TheRan]

“ Balancing happens for a reason and it's silly to avoid it just for the sake of not charging the battery to 100% (which it's designed to do).”


3.5 MV average isn’t balanced?

At 80%, no, but it could be much worse at a lower SoC under load.

[JaimeC]

Here's something I've always been wondering about.  Does the cell balancing ALWAYS happen at 100%, no matter how it gets there?

What I mean is, if I'm at an L2 station plugged into the 6kW charge tank and I leave it long enough to reach 100%, does cell balancing occur?  Or does that only happen on the slow, overnight charging done via the default onboard charger?

[NEW2elec]

As Brian Rice said, it's the BMS that controls the charge function.
With a Kill A Watt meter you can watch it balance when it shows 100% but the charge light is still blinking.  On the app the mV reading goes down.

[DerKrawallkeks]

@JaimeC
I am not splitting hairs. There is a big difference in the aging of the cells between 60% and 50%. That's why it makes no sense having them sitting at 60. The central graphite peak (in the differential voltage spectrum) is located at pretty much exactly 55%-60%, depending on conditions. No need to stay above it, when you can have much lower calendar aging at just a few percent lower storage SoC

(Taken from "Aging of Lithium-Ion Batteries in Electric Vehicles" PhD at TU München)
And about storing at 20% SoC: From a cell-standpoint, there is no damage from sitting at 20%. It's actually almost the best way to store a cell (storing at 0 SoC is kinda risky), as you can see in the diagram as well.

@princec As you can see in the diagram, the aging roughly doubles from 50% to 60% (look at the blue lines for 25°C storage). I think we can call this a big difference, or no?

@NEW2elec Financial angle is correct of course, if you have warranty. But Zero recommends keeping the bike so full only because of trouble with dying bikes due to vampire drains and other problems. It's so they don't get bad press and legal problems.
If you're out of warranty (and even within), charging and storing at high SoC causes significantly faster aging.

@JaimeC
@ TheRan Bringing it to 100% percent just before a long ride is fine, I'll not get crazy here. These batteries are there to be used. But from a technical standpoint, charging it to 100% causes significantly more aging to the battery, EVEN if you immediately discharge it afterwards. Look at the massive differences between charging full (4.15V for a Zero) compared to just slightly lower.

(taken from Battery University Website)

@ESokoloff 80/40 %SoC is definitly not easier on the battery than 70/30 % SoC, as you can see here

Look at the 41% drains @3.9V and 4.1V, that's exactly the conditions we're talking about. Significantly worse for the 80/40 % SoC cycling

[princec]

Excellent graphs, great find. It should be noted that the Y axis on those graphs does not start at 0 - so the relative differences look much larger than they actually are - eg. the difference between 50% SOC and 100% SOC storage is only actually 2.5 percentage points - it might be that it is simply more convenient to have the bike charged to 100% to make it more useful to ride than worry about losing 2.5 miles of range over the course of a year. Myself I tend to leave mine at whatever I get home at and only plug it in to charge overnight (so it'll get stuck at 100% for a few hours) if I'm reasonably sure I'll be going out on it the next day in the morning. Usually.

Cas

[DerKrawallkeks]

Yup, I agree it makes sense to not worry too much and just use our batteries;)
It's just maybe good to know what's good and bad from the technical background, and that some of the things we do aren't good. I also charge by battery full and drain it completely when I have a long ride and no time, but it's still just nice to know the effects of how we treat the battery.

About the y axis, Yes the y axis doesn't start at 0, which is usually important in statistics.
Here, I do look at the aging, so the few percent at the top getting lost. And if that increases from 2.5% to 5% let's say, that's only ca 2,5% difference overall, but it's a doubling of the aging speed. The battery will be in a similar condition after 5 years, as it would otherwise be after 10 years.
Also the first diagram only shows aging during a few months. This means all these small numbers of like 2,3,4,5% aging actually mean 10, 20, 30% in the timespans we care about, which might be 5-10 years.
For example 4 years of aging at 95% remaining after each year means you have 81% life left after just 4 years! At 97,5% remaining each year, it's 90%.
(The exact numbers in the diagram are not representative of our bike battery aging, it's the same cell type but the temperature much higher at 25°C)

[princec]

I notice the graphs are showing evidence of flattening off though, as time advances, and I think that's been borne out by Tesla's data on the matter (sorry, no citation to hand). IOW the initial wear is much faster than the wear in years 2, 3, 4, and 5. Otherwise Zero wouldn't be offering the 5 year battery guarantee knowing that half their packs were going to come back at 79% capacity...

As for myself ... I plan to just use it and abuse it like any other bike. But I'm also thinking that this time around I won't just sell the bike on, but I'll hand it down to the Mrs., and she can ride it for a few years until the battery is down to 80% initial cap, and then my cunning plan is to replace that battery with a brand new one, ending up with an SR/F Premium that's more or less as good as new for about £6k, and keep the old one to use as an absolutely enormous solar storage battery (I could run our house for half a day at full tilt on that), saving me a fortune. Win!

Cas

[Richard230]

I continue to be impressed with the 2014 Zero S with PT (built in 2013) that I gave my daughter. It has spent most of its life plugged in all of the time (which may have killed at least one OBC). When we ride together both of our SOC displays show similar percentages when we reach our destination (within 1%), even though my battery pack is said to have a slightly larger capacity than hers. Although I note that her battery tops out a 117V when her charger stops, while mine stops charging at 115V. So that might make up for the difference in battery capacities. 

[princec]

It does seem to be the case that either you're lucky and get a battery that will last forever, or you get one with a slight manufacturing defect in a single cell that brings the whole thing down eventually. And the more cells there are in a battery the more likely it is that one of them isn't going to be perfect when it comes out of the box.

Either way it also seems that the real weakness is the OBC, MBB and BMS electronics with Zeros, which seem to blow on a regular basis... looking after these rather expensive and apparently non-modular components might be the smart move rather than trying to baby the battery.

Cas