4.2V (full charge) damaging even at short periods of non-use?

How-Tos & Esk8 mechanics
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hi there, guess this has been discussed ad nauseam, but this specific question has never been asked: is leaving a battery at full charge for a day or two (charged to 4.2v per cell) linearly or exponentially proportionately damaging compared to leaving it at 4.2V for several months?

the idea is this: I try to avoid ever having my boards stand at full charge even for a day and I get really nervous when I don’t use it for two days while being fully charged. is this reasonable? this is reasonable if the correlation between full charge damage is linear across time. but, is it?

so does the math really go like this: damage(1day)=x and damage(30days)=30x

or is the curve more like damage(1day)=0.1x, damage(2days)=0.11x, damage(15d)=x, damage(60d)=10x and so on…?

this is important cause if the correlation is exponential (the more time you let it sit at full charge, the worse the chemical damage will get, squared) - then it does comparatively way less damage for shorter periods (which would be desirable) compared to longer periods. if it is linear, it is best to never leave the battery at full charge, ideally not even for hours, ideally ride when it’s done charging and balancing, but this is not very practical.

so how are things really?

TLDR Timmy left his board at full charge for one day every 12th day in 2022, so 30 times that year. Jimmy though decided to never leave his board at full charge, but had to travel some place and did not discharge it and left it fully charged for storage for 30 days before coming back.
Did Jimmy damage his board’s battery more than Timmy in 2022? or the same? what about a 90 day net (left at full charge-) time over a span of 5 years, still the same? about the same? more damage for the continuous full charge storage?

I’ve never seen this discussed… is there even data out there on this? batteries are the most expensive part in electric mobility, this matters a lot…

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Months is worse. Think of 4.2V as the max voltage of the cell where all it wants is just to start discharge. Can’t pretend to understand all the chemisty but it wears on the cell to be kept at 4.2V. I work for a lion module manufacturing company and we dont allow our cells to be charged passed 4.15V. Just not worth it.

Cells are individual beeings so you can’t really quantify it that way. For your specific cell type it has x wear while another cell has y wear.

Solution is just to hava decent BMS that cuts of at an appropriate level for the cell to make it last as long as possible. (If you favor that over the extra few % you get from charging it full)

Generally, storage voltage is around 3.3-3.7V tho. Depending on what cell.

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I don’t think you read my question right, maybe it was a bit convoluted.
everyone knows that high voltages put wear on a cell, compared to lower, even slightly lower voltages. nobody seem to know though if consecutive time on 4.2 has an expoential effect on cell chemistry wear compared to non consecutive time.

to put it as short at possible: is 4.2V for 30 single days, while each of the days may be a couple days apart exactly as bad for the battery as leaving the board at 4.2v for 30 days straight?

if the wear is linear, it is best to simply never leave the battery at 4.2v, maybe even not to charge it to 4.2v in the first place as you stated, but if the correlation is exponential, a couple days at 4.2v does comparatively little to leaving it for longer periods of time, the function would be exponential in this case.

I think many assume the the correlation is exponential, as everyone seems to suggest not to worry about charging a battey full and using the device a day later, even if you do this many times throughout a year or 5 years of use. but if the correlation is linear, this advice is big BS, and after 5 years you add up the days you left it at 4.2V, and you have ruined your battery cause it was ultimately the same as leaving your battery at full charge 90 days straight, even though you left it full only every other day, as everyone suggest would be no issue. did I come across?

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again: worse, or worse squared?

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one more practical real world thing to consider, and it’s the actual reason for this post: one of my boards has been at full charge (I usually try to avoid it, as I said earlier) for two days now, I wonder if I damaged the battery in it by either 10%, 1%, or even only 0.5% compared to leaving it fully charged for 20 days straight. if it’s 10% the correlation is linear, if it’s 1% or 0.5% it is exponential and I need not to worry about leaving it for short periods of time fully charged at all, or, well, technically exponentially less, I guess.

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In my opinion this is worse. Not sure exactly how much worse, but its worse.

A battery doesnt want to stay at 4.2 and there is very little capacity there so it will self discharge slowly from that level of charge durring your 30days and very soon will be around 4.15 where the silf discharge will lower dramaticaly as well as any damage being done.

So point here is to keep it at 4.2 you will need to hook it up to somesort of charger/power supply

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ok this is a nice addition to my question, I should set up the comparison assuming the cell would stay at 4.2v (say a charger stay connected the whole time to keep it at 4.2v) I just want to know if cumulative high voltages spread out through time are linearly as damaging as continuous high voltages concentrated to one block of time.

if it is linear, fully charging your board and not using it for a day every other day or week is equally as bad for your battery over a span of 5 years as leaving it on a charger for the same amount of time by mistake…

so yes we need to compare apples with apples and not oranges there :wink:

my gut tells me the correlation is technically linear, but people still recommend not to worry about fully charging your devices as if you don’t use them, they will self discharge anyways and not take too much damage, while also assuming you disconnect the from their chargers after charging more often then not.

it’s still misleading, as it presumes an exponential correlation where there is none. tbh I tought the correlation is exponential, as in: 1 day at 4.2V does close to nothing (say 0.1x) compared to 30 consecutive days at 4.2V (30x) that’s a factor of 10 in damage difference if it’s exponential, but I fear it’s really linear, and then @linsus advice makes a lot of sense, and common sense about “not to worry about 1 day @full charge every other day” is complete nonsense.

It also means I will ride my board now cause I feel the 4.2V anxiety right now :wink:

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Could charge to 4.1 and not think about it.

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IMO the damage (loss of capacity and internal resistance increase) occurs so slowly while in storage that it doesn’t really matter…as long as the cell is kept at room temp or cooler. Cycling the cell causes so much more damage.

But the limited data I’ve seen about this indicates that the capacity loss in storage is linear over time since aging is charge level dependent.

None of the papers had data for less than 2 month increments though. That is, the loss over the first 24 hours couldn’t be compared to loss over 24 hours after a week or a month in storage. Only the loss at 2 months, 4 months. 6 months, etc.

One thing to consider…
I think that the damage while in storage will be greater for a cell charged each day for a month vs one charged and left in storage for a month. This is because the charger keeps bringing the cell back up to a higher charge level (which accelerates aging).

So IMO the important issue is not the activity curve for the aging mechanisms during storage but how often the cell is charged over the same time period.

Otherwise I think we can assume that the aging is fairly linear over time in storage and very slow. I’ve had cells fully charged and put into storage for about five years with less than 15% loss of capacity.

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If the charger doesn’t eventually shut off the charging current that will really speed up aging of the cell. Most chargers will shut off though at some point (based on time, voltage, or current).

It’s usually only the constant-current power supplies being used as chargers that keep trying to charge the cell for as long as it’s connected. Any device labeled as a charger that does this is a piece of junk IMO.

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We recently completed 10.000 cycles of a specific cell in our lab.
Capacity at this stage was about 70% of the original. (4.15->3.1V)
Would be intresting to do comparative tests with 4.2V and see the difference. Problem is that 10.000 cycles takes a loooooong time xD.

I will pass along the question to our chemist and see if she has a more clever answer.

Temperature probably more then anything else causes the most wear.

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Would externally heating a cell cause as much increase in resistance and loss of capacity as heating from charging/discharging?

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I only charge to full when balancing. I almost never discharge lower than 20percent. When I balance, I discharge to less than after a day. This includes all devices. I think all chargers should have switch for 80ish percent. Or maybe an external device that shuts off there. I never fast charge. I limit my draw to a reasonable level.

I now avoid any riding on hot asphalt as it sapped my batt real good. Dont know about cold. Also wouldnt use right after charge, even to 80 percent. Hope my paranoia pays off.

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So my collegue came back to me and said this;

Its hard to ummarize a generalisation for the topic but wear gets exponentially worse with increasing SoC.

My guess this is primairly in function with cycling and not a resting voltage.
pushing the last few mV seems like a bad idea in relation to cyclelife regardless.

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I don’t think you should worry about riding on hot asphalt, unless you go very slow very long, the wind is going to cool the system down enough. but when you stop, or even charge, make sure it does not stay in the sun. I ruined quite a few batteries not doing this, but now they seem to stick along much longer. never leave your board in the sun. I keep wondering how e-bikers get away with not caring where they leave their bikes (usually out un bare sunlight). I think I might also have really degraded one battery on an old evolve board (yes it was my entry drug) by riding it in -15deg celsius and then fest charging it while still being way too cold for the current, and I don’t think those older models protected for this kind of situation.

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this is the kind of answer I was hoping for, looks like the recommendation of at least bioboards regarding fully charging seems is valid there: they recommend to fully charge (and stay plugged for several hous, at least 8 I think) only every 7th-ish use to let the cells balance. one of my boards still has excellent range even though it was used a lot but the battery was used close to ideally in this case, a plutonium 2, always close to 50% when not used, never charged below room temperature, never left in the sun, never charged in the sun, always stored at room temps, balanced every 8th charge, used close to immediately after full charges +balancing. a lot of work if you ask me, there should be routines in modern electronics to make sure this “petting” of our batteries gets automated, maybe presets inside charge electronics which warn you when you attempt to charge your battery at wrong temperatures? alarms when you accidentally leave the board in the sun? no idea. I mean how much does a little pc speaker weigh to be included in your board, it starts shouting annoying tones when your battery goes outside your predefined params… I mean teslas even cool and heat their batteries to help them stay cozy, we have nothing like this, yet, do we?

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If the cells are new, chances are your BMS wont need to balance for a long time. Its when the cells start to wear differently that they might create imbalances. A charger that needs to “stay plugged in” is just a bad implementation. There shouldn’t be a “done” indication if the pack needs balancing. Furthermore, if the BMS is worth its salt it will do balancing at rest, meaning when the cells aren’t in use the BMS will start bleeding cells if they differ too much. That way less balancing will have to be done in a charge cycle. (pending that the pack as a whole is OK obv.)

Most of the things you point out are basic functionality in a cell stack monitor, monitoring voltages, temps, balancing etc . If your hardware dont work with these fundamentals I’d say they’re not doing their job.
I guess thats part of the trade of with x brand china stuff. Active heating/cooling is a different story tho. I’d say that thats outside the scope for a eboard.

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Tarmac reaches 165 degrees here. That was almost too hot to touch the enclosure after a mile. Charge seemed to melt away.

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I often wonder about heatsinking the battery.

Midsummer, here in SW Florida, midday cruises, upon my return I’d flip board on workbench, and Use an IR temp gun on the whole board. The enclosure directly over singlestack battery, which is resting on 10mm of neoprene foam, was and is consistently 5f hotter than the enclosure further away from battery, opposite the esc, and both were far lower temp than the new black asphalt i was riding over.

The Nissan Leaf EV had an air cooled battery and had serious longevity issues.

Perhaps a thermally conductive foam to fill between cell voids, and be in contact with the enclosure, and deck, can both add some shockproofing, and wick more heat from cells.

Even though my neoprene foam battery padding is insulating, not designed to be thermally conductive, It is conducting some heat from cells to enclosure, even on the hottest days midsummer, midday.

My fiberglass enclosure is still ‘Volan green’, not painted black, so it rejects more road heat, but also has less emissivity for radiating internal heat to exterior than a flaT black enclosure.

Battery heating will likely be less of an issue as more cells become tabless, have lower resistance and generate less heat charging and discharging.

Im only a year deep into Esk8, but prior to this I was 12v offgrid leadacid battery guy. Wire gauge was not about what amperage can the wire insulation safely handle before melting, but what gauge copper can I afford to use and bend to fit in the shortest possible circuit run between load and source, with fewest connections, for minimizing resistance and voltage drop.

Every 12vdc device works far Better at 12.8v than it does at 10.5, So 10 gauge for a 15 foot run to a 4 amp fan was not unreasonable.

An 8gauge run from a 100 watt solar panel 25’ run to a MPPT charge controller was far more effective than 12 awg, at getting fickle lead acid batteries to as high a state of charge as possible, as soon as possible, as chronic under charging is the bane of lead acid in deep cycle applications.

Wasting battery power heating wires and connections were to be avoided as much as possible.

I had difficulty breaking this overgauge mentality in esk8.

In a tight enclosure where esc and Battery is making heat, iI’d prefer the wires to be wicking heat from connections, not adding to the heating within because technically a lighter gauge and 200c rated insulation can easily handle the expected amperage, and higher voltage means less voltage drop.

My 5.2 ah 10s2p has 0.1 copper nickel 0.1 nickel plated steel sandwich, and 10awg, as does my 10s1p, asI want as high a voltage as possible reaching ESC, not wasting battery power heating the wiring to and from, adding heat to an overheated enclosure…

I’d like to think it has improved performance and longevity.
I can’t see how it could not, other than a minor amount of added weight.

I do try and charge to 4.1vper cell and then upto 4.2 right before a ride, but often just 4.195v them disconnect and let it rest there overnight. Usually 4.19 10 hours later.

The 5.2ah 10s2p has to have well over 2k miles/3K km on it.
I returned slowly to find a 32.5 rebound voltage last evening, and it took 4.6ah to get back to 41.95v. It seems to be performing well with little capacity loss so far.

edit/add Just ran my battery from 41.94 to 33.5v midday, 80f ambient, full sun.

Immediately placed board on workbench and measured, hunting with ir gun for highest reading…
Wood away from enclosure… 82.5f
enclosure at leading edge…87.5f
Enclosure directly over battery, 92.5f.

My enclosure is only held to deck with 2 full size gaskets by 3 velcro cinch straps. Takes me 10 seconds to drop and Flip enclosure.
Hottest spot i could find on battery’s heatshrink, side facing deck, but with no thermal connection to deck, was 124.5f.

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Wasn’t your question about whether the aging at higher voltages (when charged) changed over time or was linear?

If you were just wondering if aging happened faster as the storage voltage got higher then, yes, that’s absolutely true. But not by a huge amount.

For example, assuming storage at room temp researchers found that cells like the ones we use only had about a 7% loss of capacity after 10 months at full charge. If charged to about 30%-50% there was about a 3% loss.

The internal resistance increase at full charge over ten months of storage was about 12%-17% (varying based on type of cell) at any reasonable charge level. There was very little change from 30%-100%.

For some people, a loss of an additional 4% of capacity, when going from storage at 30% to 100%, wouldn’t even be noticeable.

While storage at 30%-50% does help some it just doesn’t seem to be that critical. That’s been my personal experience too. I’ve had cells stored fully charged for about five years with only about a 15% loss of capacity. Not great but…hey…it was five years and that’s at least four years longer than any cells should be stored IMO. They’re happiest when used. :slightly_smiling_face: