do you guys leave your batteries fully charged if not riding for a long time?

[Glock43x]

I usually leave my EUC's at around 60% in the winter.

[Tawpie]

If I'm not going to ride a wheel for more than a couple of weeks I try to get the voltage down to 60% or lower before storage. I don't worry about leaving one at full charge for a few days—but it takes extraordinary circumstances for me not to ride at least every other day. I'm a junky.

[alcatraz]

What's a long time to you?

I saw some guys on the forum unable to power on their wheels after 1-2 years, possibly because their batteries hadn't been charged enough during that time. Now they need to service them or find new packs.

So yes, on an individual cell level, aim for 50% but it's not a good idea to ignore the wheel for a year or two. It could show 50% charge level when powered on but with the dumb bms' in there we can't tell if a cell group has deviated during that time. In which case it's better to ride+charge than store the wheel. However, when it starts to deviate it's only a matter of time before there's a bigger problem. You're damned if you do, and damned if you're don't.  Batteries are a bit hit and miss. Hope you get a good pack that lasts a long time. The cells need to be well matched for that.

[mrelwood]

Some EUCs have phantom drain that consumes battery (very slowly) even when it’s powered off. Some wheels only go to “sleep mode”. So unless one is sure that this doesn’t happen in their wheel, one should check the voltage at least every few months or so.

I store at 40-60% as well. Although, the concept as a whole has been a bit alien to me ever since I got myself a studded winter tire…

[Cerbera]

As a quick aside, how often, as a rule, @mrelwood do you find yourself out on the A3 these days ?!

 

[MetricUSA]

Never leave wheels alone uncharged that long, over several months...that definitely kills the battery, need to charge wheel every one or two months... 

Out side of that... I don't try to charge until several hours before I need to, especially on a cold 'winter' day... You'll have warm battery before going into the cold... 

Edited November 1, 2022 by MetricUSA

[Chriull]

9 minutes ago, MetricUSA said:

Never leave wheels alone uncharged that long, over several months...that definitely kills the battery, need to charge wheel every one or two months... 

That's no problem for lion - just some wheels like z10 and now some kingsong that don't turn off sometimes kill the cells...

If one has any other "normal" wheel it'll be better to just check voltage regularly and _only_ recharge a bit once needed...

Edited November 1, 2022 by Chriull

[mrelwood]

15 hours ago, Cerbera said:

As a quick aside, how often, as a rule, @mrelwood do you find yourself out on the A3 these days ?!

Haha! Maybe once or twice a year...  

[Cerbera]

10 minutes ago, mrelwood said:

Haha! Maybe once or twice a year...  

I still remember my little Airwheel with great fondness. It wasn't very fast or very powerful, and the smallest of potholes could be your undoing, but it was a relentless little trucker that just... kept... going. Until its poor little battery capacity shrank to so little to be of practical use, so I donated it to a friend in the Navy, who would use it to roll around ships all over the world !

[mrelwood]

A3 or an EUC? The same description seems to apply to both. 

[RagingGrandpa]

On 10/28/2022 at 11:34 PM, Glock43x said:

I usually leave my EUC's at around 60% in the winter.

Sounds fine.

My favorite advice is:

On 5/6/2020 at 11:41 AM, RagingGrandpa said:

Don't charge after a ride, unless you're going to ride again immediately. (Minimizes storage SOC.)

I truly think this is all that would be needed for most EUC owners to keep their packs happy. If they knew this and nothing else, I think we'd be in a better place than today.
Perhaps some Z10's would self-discharge during long-term storage and need manual recovery... but if you put a Gotway in the basement at 3.3V/cell (unridable), come back 6mos later and I think you'll find it happily resting at 3.0 and ready to recharge.

 

On 11/1/2022 at 9:41 AM, MetricUSA said:

need to charge wheel every one or two months

No way! 

Modern EUC's have very little standby discharge- you might lose 10% SoC per year. 

We want to store cells at a low voltage, just never below 2.0V per cell. It's a wide margin, considering that EUC's call 3V/cell "0%". 

If you're concerned, set a reminder to powerup the EUC after 2mos and inspect the voltage. But I expect you'll find it hasn't changed much.

[mrelwood]

 

3 minutes ago, RagingGrandpa said:

We want to store cells at a low voltage, just never below 2.0V per cell.

2.5V is usually the low voltage cutoff advised by the cell manufacturer, at least with the cells that most EUCs use.

 Other than that, I agree.

[RagingGrandpa]

2.5V "normal area" to leave some margin before the "damage area," yes  
 

On 5/14/2021 at 7:38 AM, redsnapper said:

https://link.springer.com/article/10.1007/s41918-019-00060-4

 

Edited April 24 by RagingGrandpa
(img url)

[0000]

50 minutes ago, RagingGrandpa said:

2.5V "normal area" to leave some margin before the "damage area,

That image would be improved to include some nuance as what defines safe and damage as it relates to capacity degradation since we're kind of on that topic here. I don't remember if I linked or talked about this info here or another forum, but cycle depth plays a notable part in increasing the amount of capacity degradation experienced by cycling lithium ion batteries. A summary:

Quote

Section 6.6 Conclusions
Cycle depth has been identified as a major influencing factor for battery degradation. With higher cycle depths, capacity fade and resistance increase are aggravated. In particular, the resistance increase has revealed a strong dependency on cycle depth and only a small dependency on <high> SoC <such as 4.1V, 4.15V, and 4.2V>. Moreover, the resistance increase is mainly caused by rising charge transfer resistances of the NCA cathode. The increasing resistances lead to higher losses and a lower energy efficiency. This has to be considered when designing cooling system for EV batteries. Similar to the calendar aging studies, no direct correlation between resistance increase and capacity fade could be identified. Regarding the resistance contributions from the anode, there has even been a reduction at the beginning of the cycle aging study when the cells were cycled at 40°C or 25°C – although the capacity was decreasing.

You can also check out Section 6.5.3 for the Impact of Cycle Depth results for the data leading to the conclusion above if interested. I know there's quite a bit of nuance in the performance and aging of cells based upon the blend of chemistries used, particularly as newer generations of lithium ion batteries improve; however, I believe the trend they found in this study is generally true for all lithium ion batteries.

In other words, the tilt-back protection at ~3.2V (depending upon your wheel/firmware) is also somewhat protecting the cells from prematurely losing capacity by preventing higher  depth of discharges all the way to the 2.5V "safe" discharge range. To say nothing of storage voltage, charging to 100% or 4.2V/cell is significantly less damaging in terms of accelerated capacity decay compared to repeatedly cycling your batteries to 100% depth of discharge or 2.5V from 4.2V. So in terms of battery longevity, it is a good thing our motor controllers do not allow such a high DoD.

Edited November 2, 2022 by Vanturion

[RagingGrandpa]

On 11/2/2022 at 5:40 PM, Vanturion said:

https://mediatum.ub.tum.de/doc/1355829/document.pdf

Great paper!

Section 4 has the meat, with regard to storage.

It's more evidence for the prevailing wisdom: store at low voltage (less than 3.5V/cell) and cool temperature (~10°C).

...because it minimizes capacity loss:

...and minimizes resistance change:

(Their definition of SoC was this.)

 

On 11/2/2022 at 5:40 PM, Vanturion said:

cycle depth plays a notable part

During use!

But during storage, there is no cycling.
Low is good. Perfect to be between 3.0 and 3.5V.

 

Edited August 17, 2023 by RagingGrandpa
(img url)

[mrelwood]

1 hour ago, RagingGrandpa said:

2.5V "normal area" to leave some margin before the "damage area," yes  

The source I’m most familiar with paints a different picture:

https://batteryuniversity.com/article/bu-501-basics-about-discharging

Under normal load they suggest not going under 3-3.3V, which is exactly the range that EUCs prevent you from going below.

[0000]

38 minutes ago, RagingGrandpa said:

During use!

But during storage, there is no cycling.
Low is good. Perfect to be between 3.0 and 3.5V.

Yes, thanks for the clarification.

One interesting anecdote I noticed, primarily from following all of Pajda's lithium ion battery cycle tests on endless-sphere, is that Panasonic cells (brand used in the study) tend to perform the worst in cycling and capacity degradation tests in comparison to basically all of the other manufacturer's comparable 18650 and 21700 cells. I've always wondered what the implications are regarding their prolific use on Tesla vehicles if there are better alternatives, but then again, all of their cells are actively thermally managed so it stands to reason that the horrible degradation they exhibit, in relative comparison anyway, without thermal management isn't the same as how they typically perform in their automotive applications.

Since I've just never seen comparable capacity degradation tests with thermal management and PEVs tend not to use such expensive and weighty systems, I'm just left thinking Panasonic cells are basically the last cells I would want to use on any kind of PEV build. Anyway, not really related to OP's question. I think your links from the study definitively answers the question of ideal lithium ion battery storage parameters

Edited November 2, 2022 by Vanturion

[Tawpie]

so... store in a cool dry place, below 3.5V/cell. For my 84V KS wheels that means below 70V, which is 50% indicated (assuming that 3.0V is 0% indicated). For my Sherm, 0% indicated is 3.3V so I want to be below 20% remaining to have my cells at 3.5V (84V for the packs).

For simplicity to guide my actions I'll just use voltage... store my 84V wheels below 70V (20*3.5) and my 100V below 84V (24*3.5).

[mrelwood]

6 hours ago, Tawpie said:

so... store in a cool dry place, below 3.5V/cell. For my 84V KS wheels that means below 70V, which is 50% indicated (assuming that 3.0V is 0% indicated).

16X has 0% at 3.15V/cell, so 50% should be at 73.5V.

Although this amount of detail will never exhibit noticeable differences. 

 

[Funky]

I normally ride down to ~55% and then store it. Over winter if i'm not riding i check battery levels once a month.

Even if i don't ride for week or two. I normally go for "fun" ride till i get down to 60%. Otherwise i don't like to keep it full even for a week or so. Fully charged for 1-3 days is okay with me.

And when i charge - i charge it to fully every time. And when charger turns green i leave it charging extra 2 hours normally. So cells get balanced correctly and healthy.

[Funky]

Why "exactly" those numbers? I normally try to store closer to 73-74v / 55-60% battery. And my room temp normally is 25-27c.

I thought anything below 70v / 50% would be worse. That's why i try to do 73v / 55%.

 

Also question.. If my battery sits almost all the time at 55-65% isn't that also kinda "bad"? If i'm not riding i normally go for longer ride and then keep the wheel at those levels.. That's why i'm asking.

Edited November 7, 2022 by Funky

[RagingGrandpa]

1 hour ago, Funky said:

I normally try to store closer to 73-74v [3.7V/cell]  
I thought anything below 70v [3.5V/cell] would be worse.

We're splitting hairs. Your way is great.

In the study we discussed, at 25°C, 3.7V gives 1% more capacity loss over a two year storage duration, than 3.45V. That's negligible.

And there's no harm in lower voltages, as long as we're above 2.5V. 
(I think there is no practical way to discharge an EUC to 2.5V, since alarms and tiltback come at 3.0V or higher.)
 

1 hour ago, Funky said:

If i'm not riding i normally go for longer ride and then keep the wheel at [about 60% SoC]

That's great! 
"Don't store full."

[Funky]

12 minutes ago, RagingGrandpa said:

We're splitting hairs. Your way is great.

In the study we discussed, at 25°C, 3.7V gives 1% more capacity loss over a two year storage duration, than 3.45V. That's negligible.

And there's no harm in lower voltages, as long as we're above 2.5V. 
(I think there is no practical way to discharge an EUC to 2.5V, since alarms and tiltback come at 3.0V or higher.)
 

That's great! 
"Don't store full."

Good thing i don't need the capacity.  I charge my wheel only twice a week. If i'm riding everyday. So i would never notice any lost range.

And how about that question - keeping batteries at 55-65% most of time. It doesn't harm the batteries somehow? (Nowadays i charge fully, then go for a "fun" ride down to ~55% and store it 1-2 weeks.. Till next ride. I try to ride at least twice a month. Because i don't really "need" to ride anywhere at the moment.)

Edited November 7, 2022 by Funky

[RagingGrandpa]

5 minutes ago, Funky said:

keeping batteries at 55-65% most of time. It doesn't harm the batteries somehow? 

No harm. Especially if in a cool temperature (0 to 25°C).

[Funky]

Just now, RagingGrandpa said:

No harm. Especially if in a cool temperature (0 to 25°C).

I thought that batteries have some kind "memory" issue or something.. If they are kept at the somewhat same voltage. Like it was sitting at 73v for 2-4 weeks charge fully for 1-2 days at 84v. And then it's again sitting around ~73V. It really doesn't have any kind of problem/danger?

Or was all that only in my head?  

Ohh and i have another question. Lets say i haven't used the wheel for about 3 weeks. It has been sitting at 73v. And then i go for a ride without charging it fully before. And then again store it away for 1-2 weeks. It also have none danger?

In other words: Waking up wheel mid sleep for little ride and putting it back to sleep - without charging it before said small ride?  

Edited November 7, 2022 by Funky