Charging/battery health questions

[AtlasP]

Given the following premises which I've read on here:

• Batteries degrade over time due to the combination of just storing charge and also/in particular in response to charge/discharge cycles.
• It's best to store the battery at between 40-50% to 80-90%, and therefore it's better to come back from riding at 50% and let it sit like that overnight and charge in the morning, rather than charging it right when getting home and sitting charged overnight.
• Fast charging puts more strain/wear on battery. (Although I've seen this debated. Is this true?)

Then I have the following lesser-of-two-evils-type questions:

1. If I charge the battery more full (90-100%) I can get through two days' usage before charging whereas if I charge it less full (80%) I can only get through one/have to charge every day. Is it better to charge it less full (80%) but have to top up every day (lower charge amount but more charge cycles) or to charge it more full (90-100%) but only have to charge every other day? (Essentially, what is the impact of more frequent small top-up charges? Is this still bad from a charging cycles perspective? Or because they're small--like going from 60% to 80%--is this less bad?)
2. If I wait to charge until the morning then I would often have to rely on quick charging to complete the charge before leaving. Is it better to let the battery sit uncharged overnight but to have to rely on quick charging in the morning, or to trickle charge overnight? Or I guess another option would be to charge to 80% every night, then just top up above that in the morning if/as necessary? Which of these would be best?

[Chriull]

On 5/28/2019 at 11:18 PM, AtlasP said:

Given the following premises which I've read on here:

• Batteries degrade over time due to the combination of just storing charge

If the charge is high enough. At 100% it degrades much more than on 40%. And temperature is an important factor.

Temperature	40% charge	100% charge	Table 3: Estimated recoverable capacity when storing Li-ion for one year at various temperatures. Elevated temperature hastens permanent capacity loss. Not all Li-ion systems behave the same.
0°C	98% (after 1 year)	94% (after 1 year)
25°C	96% (after 1 year)	80% (after 1 year)
40°C	85% (after 1 year)	65% (after 1 year)
60°C	75% (after 1 year)	60% (after 3 months)

from https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

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• and also/in particular in response to charge/discharge cycles.

Where here full charge/discharge cycles count. So 50% to 0% count only half...

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• It's best to store the battery at between 50%(?) to 80-90%, and therefore it's better to come back from riding at 50% and let it sit like that overnight and charge in the morning, rather than charging it right when getting home and sitting charged overnight.

Exactly.

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• Fast charging puts more strain/wear on battery. (Although I've seen this debated. Is this true?)

No. But this depends mostly how one defines fast charging. For most Li Ion cells some 0.4-0.5C are recommended. With the stock chargers one reaches about 0.1C, with the 5A chargers one stays still (with most of the big battery packs) well below the 0.4C. I have not found any study that there will be any notable difference. Just once one charges above 1C degradation is noticable. This "fast charging puts more strain/wear on the battery" comes from the RC groups, where LiPos are charged at really really high C rates (something >5C?).

How to get this C Rate: One needs to know the capcity of the wheels single cells. They are mainly ~3000mAh(3Ah) or ~3500mAh(3,5Ah). And the second number one needs is the cells in parallel. Then one multiplies this number - the cells in parallel with the individial capacity.

For an KS18XL (and high capacity MSX?) that's 6 cells in parallel with about 3,5Ah makes 21Ah. The "C Rate"  is the charging current divided by this 21Ah . With some 2A charger it is 2/21 ~ 0.1C, with 5A 5/21=0.24C.

 

A bit more on fast and ultra fast chargers: https://batteryuniversity.com/learn/article/ultra_fast_chargers

As seen there, the high burdens while discharging (riding) the wheel is what could make one concerned... Not if one charges at 0.1C-0.4C. I'd assume even (almost) up to 1C should be neglectable compared to the discharge burden effects...

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Then I have the following lesser-of-two-evils-type questions:

1. If I charge the battery more full (90-100%) I can get through two days' usage before charging

Then you had it at ~100% just before the first ride. After the first day its well below (~60%?) and after the second day at around 30%?! Sounds like a great usage pattern. Just the time the wheel sits around high charges counts!

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1. whereas if I charge it less full (80%) I can only get through one/have to charge every day.

Whereas in this example the wheel sits more time at this ~80% charge. Which should have much less effect than sitting half to one third the time at ~100% - at least there are no real numbers of this at batteryuniversity. They just mention on one page that charging to ~3,9V per cell there is about minimal stress. And this is about 74%.

The downside on this pattern is, that its much more uncomfortable, takes much fun from riding and i could not really say if it's better or worse than the first...

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1.  Is this still bad from a charging cycles perspective? Or because they're small--like going from 60% to 80%--is this less bad?)

Yes - 60%-80% count only 20%/100% = 1/5 charge cycles.

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1. If I wait to charge until the morning then I would often have to rely on quick charging to complete the charge before leaving. Is it better to let the battery sit uncharged overnight but to have to rely on quick charging in the morning, or to trickle charge overnight?

Quicker charging in the morning is better. There is no trickle charge overnight - li ion chargers cut off, once the finished the C(onstant)V(oltage) phase. But this CV phase is when cell balancing occurs - so this should be done from time to time to keep the cells matched!

BTW: Quicker chargers have a CV phase that takes as long as the normal stock low amperage chargers. Its just the first phase with C(onstant)C(urrent) that is faster according to the current factor! The CC phase charges to about 85% and takes about 1 / "C Rate" hours for charging from 0% to 100%  this ~85%(1)

https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

 

(1) Unfortionately at least here has to be mentioned that the charge % from the wheel does not correspond to the charge state of the cells. Wheels show 100% for cell voltages above about 4,1V and 0% for cell voltages below 3,3V (3,0V for KS18XL). Wheras a full charge cycle for a li ion cell is from 100% with 4.2V downto 0% at 2.5V (2.75V for some cells). 

[AtlasP]

Chriull: awesome, thanks so much for the detailed reply! If I'm understanding correctly then I'll just wait until mornings and charge to 80% every single morning before I go out (even if that needs to be at 4-5A).

Follow-up questions:

• Is there a lower bounds to healthy storage charge? (Is for example 25 or 30% worse for the battery than 40%?)
• Is storing a little lower than ideal better or worse than a little higher than ideal or about the same? (Or is higher than ideal still way worse than a little lower than ideal?)
• If lower temperatures are better, has anyone considered some kind of very mild refrigeration to preserve EUC life or is that preposterous/overkill? Unfortunately swapping out batteries is not quick/easy and I guess chilling the entire EUC could cause condensation issues. But I wonder about like a cheap wine fridge that only stays in like the 50s (F)? Still problematic re: condensation and/or not worth it?

[Chriull]

2 minutes ago, AtlasP said:

Chriull: awesome, thanks so much for the detailed reply!

You're welcome!

2 minutes ago, AtlasP said:

If I'm understanding correctly then I'll just charge to 80% every single morning before I go out (even if that needs to be at 4-5A).

Follow-up questions:

• Is there a lower bounds to healthy storage charge? (Is 25 or 30% worse for the battery than 40%?)

You'd have to calculate from charge % shown to real cell state of charge and look it up at batteryuniversity.com. 

But from gut feeling i'd say it should be about ok for not too long time. Maybe 25% is a bit low?

And be carefull if you have a Z10 - with its high self discharge he'll drain down and stress the battery! Z10 have to be stored at higher charges.

2 minutes ago, AtlasP said:

• Is storing a little lower than ideal better or worse than a little higher than ideal or about the same? (Or is higher than ideal still way worse than a little lower than ideal?)

Pfff... I just remember in detail this 40 and 100% numbers.

[Mono]

On 5/29/2019 at 12:46 AM, AtlasP said:

Chriull: awesome, thanks so much for the detailed reply! If I'm understanding correctly then I'll just wait until mornings and charge to 80% every single morning before I go out (even if that needs to be at 4-5A).

Follow-up questions:

• Is there a lower bounds to healthy storage charge? (Is for example 25 or 30% worse for the battery than 40%?)

Probably not. My understanding of the data is that, unless below 0%, lower is probably never worse. My suspicion is that the 40% recommendation is not lower a) to make an undercharge below 0% from small drains less likely and b) because lower values don't gain a lot anyway. I also assume that a good battery management should make undercharge within a year-or-so almost impossible to happen, but not all wheels abide by this rule.

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• Is storing a little lower than ideal better or worse than a little higher than ideal or about the same? (Or is higher than ideal still way worse than a little lower than ideal?)

At 25ºC for one year we have losses of 4% at 40% charge state and 20% at 100% charge state. I'd assume the loss vs charge state curve is monotonous and convex. This means, changes at the higher charge end have the most impact: don't worry whether you are at 40 or 50%, but do worry whether you are at 90 or 100%. Similarly, I do have good reasons to believe that cycling from 0 to 50% is considerably better than cycling from 50% to 100%.

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• If lower temperatures are better, has anyone considered some kind of very mild refrigeration to preserve EUC life or is that preposterous/overkill? Unfortunately swapping out batteries is not quick/easy and I guess chilling the entire EUC could cause condensation issues. But I wonder about like a cheap wine fridge that only stays in like the 50s (F)? Still problematic re: condensation and/or not worth it?

I thought about it. But then, one obviously cannot gain a lot: one can reduce a 4% yearly loss only by so much, namely by 100% which amounts to only 4% then  Additionally, my battery sits rarely at or above 25ºC when I have the opportunity to cool it. Finally you may have to be careful about condensation water when storing it in a fridge (I don't know what the good policy is there).

[Chriull]

46 minutes ago, Mono said:

Similarly, I do have good reasons to believe that cycling from 0 to 50% is considerably better than cycling from 50% to 100%.

These partial discharge cycles are mentioned with many tables at batteryuniversity.com. But unfortionately not clearly written starting from which voltage/charge state - or i just did not get it. Will have to reread this article once again in detail.

But EUCs perfomance and safety margin depends an battery voltage! So, at least i personally try to start with a 100% charge!

... and with many wheels driving below some ~ 30% gets really bad with all the speed restrictions starting...

[Mono]

1 hour ago, Chriull said:

But EUCs perfomance and safety margin depends an battery voltage! So, at least i personally try to start with a 100% charge!

I was strictly writing about battery degradation. If you want to cycle starting from 100% for whatever other reasons, you should certainly do. After all the purpose of the battery is not to live as long as possible but to serve as an energy source with the desired characteristics.

Personally, I rarely charge to 100% and I find the dependency of wheel behavior on the charge status notable but not particularly disturbing. Above the speed of 15km/h I avoid situations where the access torque margin may become an issue anyway.

[Werner]

On 5/30/2019 at 11:45 AM, Chriull said:

But EUCs perfomance and safety margin depends an battery voltage! So, at least i personally try to start with a 100% charge!

... and with many wheels driving below some ~ 30% gets really bad with all the speed restrictions starting...

That's because of I every time load my wheel to 100% to start with full battery. I commute every day when the weather is fine and go about 30km/ day. At Friday, Saturday and Sunday I try do go with the whole energy I can get. That ends sometimes with 1 or 2 percent left which is nothing. 

A few days ago I had to go back the last 2km to get home. 

My Z10 was totally confused with it's empty battery. 

That looked then this way,  🤣🤣

 

[Olav]

2 hours ago, Werner said:

My Z10 was totally confused with it's empty battery. 

That looked then this way,  🤣🤣

 

Same thing Ian (Speedy feet) got on his Z10 when he tested his untill it couldn't be ridden anymore (and had to walk/carry it for a while to get to somewhere he could be driven home).
Thats an odd behavior though.

[hyiu00]

For most EUC rider that is no expert in battery, what happens when the battery level goes too low?  Will a normal EUC warn the rider first or it will just fail and cause an accident?  I can say that for new batteries, it should be safe, but my question is how about old batteries?  Will old batteries cause accident without warning from the EUC when the battery level goes too low?  If old batteries can cause accident, then there is still a big safety difference between a EUC and a E-scooter.  The concern is that for most rider, there is no way to tell how old their batteries can be, before they become unsafe to ride.  Can anyone give insight into what happen with old batteries as I do not have experience on?

[MaxLinux]

On 5/28/2019 at 6:56 PM, Chriull said:

Z10 - with its high self discharge he'll drain down and stress the battery! Z10 have to be stored at higher charges.

What is meant by "self discharge" of the Z10? Thank you.

[Chriull]

3 hours ago, MaxLinux said:

What is meant by "self discharge" of the Z10? Thank you.

 

[Smoother]

On 5/28/2019 at 10:18 PM, AtlasP said:

Or I guess another option would be to charge to 80% every night, then just top up above that in the morning if/as necessary? Which of these would be best?

My plan, in your situation is this (above)

I don't recall any specific advice about waiting overnight to charge, simply don't charge hot batteries.  So if you wait a bit for your batteries to cool down (say 30 minutes to an hour) I see no reason why you can't charge on the same day; I ALWAYS do, but most of my rides include a trip home in the car of 30 minutes or so, so a cooling period of sorts is built in, PLUS I don't ride that hard so my batteries probably aren't even warm.  Remember, not all riding heats up the batteries, so don't assume they are hot just because you went riding.

[Mono]

45 minutes ago, Smoother said:

I see no reason why you can't charge on the same day

The disadvantage is that then the battery sits at a higher charge all night long each night. Sitting at high charges is a main reason for battery degradation.

[esaj]

8 hours ago, hyiu00 said:

For most EUC rider that is no expert in battery, what happens when the battery level goes too low?  Will a normal EUC warn the rider first or it will just fail and cause an accident?  I can say that for new batteries, it should be safe, but my question is how about old batteries?  Will old batteries cause accident without warning from the EUC when the battery level goes too low? 

Probably all newer wheels (and at least most older wheels) have some sort of warning for low battery voltage (ie. battery getting empty). Old batteries could potentially cause an accident, the total capacity of the cell goes down and internal resistance goes up at least somewhat with age / deterioration, which may cause a much higher voltage drop at high current draw than for new(er) batteries, and the battery running out faster than you've used to.

If the current draw goes up fast (rapid acceleration, hitting a big bump requiring a sudden very high current spike that can't be handled by the mainboard capacitors alone), the voltage might drop enough to not be able to drive enough current through the motor, and the torque drops sharply, so the motor cannot accelerate to keep balance.  For new or old battery, the more empty the cells are, the less current (and power) you can draw from them without the voltage dropping to "too low" values.

This has happened in the past with wheels that have only one or two battery packs, even if the batteries are relatively new, leading to a "over-lean" or "over powering" the wheel. In temporary high power spikes, the the nominal motor powers likely don't matter that much (you can likely put 10000W through a nominal 500W motor for a very short while without any damage, if the power source, ie. the batteries can deliver that), but it depends on the batteries and mainboard capacitors / other electronics to be able to deliver that spike. So in those cases, the cause has probably been more about not having enough batteries in parallel for the high current demands, but at least theoretically, it could happen with any wheel where the batteries have degraded "enough" to not be capable of providing enough current/power.

Soo... "it depends". More battery packs in parallel can dish much higher currents, adding safety margin at the extreme power demand situations. But still, with old batteries that used to be able to do that, might not anymore. With more packs in parallel, the packs that haven't aged as fast as the others can keep up longer, they're also stressed less while in use, as they don't need to provide all the power by themselves. Still, in a totally hypothetical case, were a single faulty pack to short circuit, and the surrounding parallel packs didn't have any current limitations, that single pack could cause the destruction of them all... Of course more packs means higher price, as the batteries and the motor are usually the most expensive parts, in wheels with lots of packs (like 6P or 9P), the batteries alone are likely more than half of the cost of the entire wheel.

 

8 hours ago, hyiu00 said:

If old batteries can cause accident, then there is still a big safety difference between a EUC and a E-scooter. 

There will always be a big safety difference with a single-wheel and any two- or more wheeled vehicle. Losing power on a e-bike or scooter or such, while inconvenient, will not lead you to face planting, whereas on an electric unicycle, the only thing keeping you from falling on your face or back is the entire chain from batteries to mainboard to motor, a failure in any of the critical components on the chain will cause an immediate faceplant. Even with dual windings and redundant motor drivers, a number of electrical issues or a mechanical fault could still cause you to go splat. The more sure way to prevent that is to add another wheel, at which point its not a unicycle anymore.

But do consider that the early wheels we rode with had 350W nominal motors with a single 16S1P, 130-210Wh battery pack (and some lucky ones had wheels with 2P or even 4P battery packs ). Yes, falls and failures did happen, you could probably say that they were somewhat common place at that time, and there were even serious design faults in many wheels (like BMSs cutting power without warning at high current demand). Still didn't stop me or most of the "early" riders in these forums, though  

Whether the "risk" is worth it, is up to each individual. Was it wise to constantly ride 30+km/h on a 550W nominal motor and 16S2P packs? On a wheel that had DIY shunts in the battery pack to prevent it from cutting power, but that could lead to the battery pack catching fire if it was accidentally shorted? Probably not, luckily didn't burn down the house or end up eating asphalt and had a blast though...   Not that I'd really recommend anyone to try that, plus there's no need anymore.

Nowadays, the wheels have usually at least 4P batteries, up to 9P or maybe even more. The designs have improved a lot (not to say that there isn't always at least some room for improvement), safety margins and powers have gone up by multiples in the past 4 years. There are at least rudimentary battery and health monitoring systems in place and warnings of overcurrent and such, rather than the wheel cutting out. A vast majority of crashes is due to rider errors, full device failures are a much more rare thing. If there are more serious issues, they're usually at the very first batch (or a couple first ones), and get remedied quickly (still, I personally would never buy a new model off the first batches ). But still, any wheel could potentially fail at any time, so if you choose to ride these things, gear up. Even if and when the wheel works without a hitch, you or someone else in the traffic can make a human error, leading to a crash. I don't like to pretend that these things are "safe". If I believed that, I wouldn't ride with a motorcycle helmet, wrist guards and pads. They're safe enough to ride around in the pedestrian and bicycle traffic (there the risk is caused by the rider behavior rather than the wheel), but entirely fool-proof? Never with a single wheel.

 

8 hours ago, hyiu00 said:

The concern is that for most rider, there is no way to tell how old their batteries can be, before they become unsafe to ride.  Can anyone give insight into what happen with old batteries as I do not have experience on?

Mostly, the maximum capacity of the cells / battery goes down as it ages, the internal resistance may also go up over time. With lithium-ion, this degradation is permanent, the lost capacity of some battery types can be (up to a point) somewhat "rejuvenated" through cycling, with lithium-ion, that just makes things worse. Nowadays, at least according to Battery University, the internal resistance usually isn't that much of a problem ("There is a notion that internal resistance is related to capacity, but this is false. The resistance of modern lead acid and lithium-ion batteries stays flat through most of the service life. Better electrolyte additives have reduced internal corrosion issues that affect the resistance. This corrosion is also known as parasitic reactions on the electrolyte and electrodes. "), but will still go up towards the end of the battery lifetime. The reduced capacity will mean that over time, you won't get as much mileage out of a full charge as before, and if you're used to pushing the wheel at low battery, this can bite you. Also one or two cells might degrade faster than the rest, and that or those cells can cause the entire battery to go "bad", dropping the voltage more at high current draw, that could lead to a faceplant, and in the worst case, overheat and catch fire...

There are ways to measure the internal resistance and capacity of the battery packs and individual cell voltages to at least estimate the battery pack health. Of course, outside of measuring the pack total capacity through a Charge Doctor or similar, the internal resistance and cell voltage measurement are not something everyone can do. The BMSs could measure the individual cell voltages (some do, like Ninebot Z's?) and that information could be used to inform the rider if the battery pack doesn't seem healthy anymore. Most wheels lack any communication between the BMS and the mainboard, so the program logic is oblivious to individual cell voltages, and only measures the total voltage, which is used to tell you how much battery is left. Internal resistance measurement is a bit more tricky, and harder to implement in the wheels due to multiple packs in parallel, but could be done "by hand". The cell voltage measurement would probably be a better indication of the pack health anyway? Once a cell or a couple of cells starts to go up in voltage faster (during charging) and drop more voltage during loading, it's a sign it has deteriorated faster than the rest or has developed an internal fault that's likely not going to get any better over time.

 

As usual, most of everything above is my own opinions and conclusions. I'm not an expert on batteries or electronics. Feel free to correct me where I've gone wrong.

[Mono]

5 minutes ago, esaj said:

Mostly, the maximum capacity of the cells / battery goes down as it ages, the internal resistance may also go up over time. With lithium-ion, this degradation is permanent, [...] The reduced capacity will mean that over time, you won't get as much mileage out of a full charge as before, and if you're used to pushing the wheel at low battery, this can bite you.

What I was wondering for a while: do we see this reduced capacity always via a reduced final voltage when fully charged?

[esaj]

Just now, Mono said:

What I was wondering for a while: do we see this reduced capacity always via a reduced final voltage when fully charged?

Going out on a limb here, but to my knowledge, likely not, at least not directly. The voltage at the end of the charge comes from the charger, so it's up to the charger output voltage what the final voltage is. But, again based on what I remember reading, degraded cells also (may?) have faster internal self-discharge. This should cause the cell voltage to drop faster after charge, but it still might take a good while? Under load, the highest voltage drops faster, as the discharge voltage curve is not linear, but that could also maybe be used to measure the cell health.

Maybe software monitoring could be made based on the rate of the voltage drop after full charge (assuming the wheel isn't used straight away). Of course baselines for "normal healthy" cells should be measured first, and the software calibrated, but that might be another place where some improvements on safety could be made.

 

[hyiu00]

Thanks esaj for your detail explanation.  Now I wonder if the IPS S5 with dual motor, dual BMS, and dual battery can improve the safety of EUC as the likelihood of both sides failing at the same time should be much much lower.  Now I am wondering if anyone riding the IPS S5 have an actual situations or tests to show that this redundant design is really helping to improve safety.

[Mono]

2 hours ago, esaj said:

Going out on a limb here, but to my knowledge, likely not, at least not directly. The voltage at the end of the charge comes from the charger, so it's up to the charger output voltage what the final voltage is.

Still, if the charger is disconnected after a full charge, the fully charged battery voltage doesn't need to be the charger voltage, or does it?

[esaj]

1 minute ago, Mono said:

Still, if the charger is disconnected after a full charge, the fully charged battery voltage doesn't need to be the charger voltage, or does it?

No, if there's still been current flowing from the charger to the battery, it means the charger voltage has been higher than the battery, ie. the battery hasn't charged all the way to the full voltage. But I don't think this really tells you anything about the battery health, just that the charge wasn't 100% complete.

 

[Mono]

1 hour ago, hyiu00 said:

Now I wonder if the IPS S5 with dual motor, dual BMS, and dual battery

Claiming a "dual motor" looks like a publicity stunt to me. If true, one either carries lots of unnecessary weight, or it means faceplanting in any critical high-demand situation when only one of the motors failing. Like this, the motor-related safety is halved, as any of the two motors failing leads already to an accident.

[Mono]

6 minutes ago, esaj said:

No, if there's still been current flowing from the charger to the battery, it means the charger voltage has been higher than the battery, ie. the battery hasn't charged all the way to the full voltage. But I don't think this really tells you anything about the battery health, just that the charge wasn't 100% complete.

I just realized that you answered my question already somewhat when writing

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Once a cell or a couple of cells starts to go up in voltage faster (during charging) and drop more voltage during loading, it's a sign it has deteriorated

 

[Smoother]

4 hours ago, Mono said:

The disadvantage is that then the battery sits at a higher charge all night long each night. Sitting at high charges is a main reason for battery degradation.

I was referring to battery tempreature issues, and referenced charging to 80% in the quote, for overnight with a potential pre-ride top up.  I stand behind my statement. "A higher charge all night long" is a bit vague for planning purposes. How hi is too high?

A Toyota sales employee told me the latest BMS on Toyotas won't allow a charge over 80% or under 20%.  Within these percentage they felt battery life was optimized. I haven't confirmed his statements He actually said something like "never wear out" but that would not be possible; even age would eventually do them in

14 minutes ago, Mono said:

Still, if the charger is disconnected after a full charge, the fully charged battery voltage doesn't need to be the charger voltage, or does it?

My experience with worn out Li Pos is that they will show 4.2 V after a charge, but the voltage drops very rapidly when under a load.  This makes them useless except maybe as reserve for a flash light, but even then, a few $ will buy a good one.

[Mono]

6 minutes ago, Smoother said:

I was referring to battery tempreature issues, and referenced charging to 80% in the quote, for overnight with a potential pre-ride top up.  I stand behind my statement. "A higher charge all night long" is a bit vague for planning purposes. How hi is too high?

We know two numbers for a yearly capacity loss at 25ºC: 4% at 40% charge state and 20% at 100% charge state. I would expect at 80% charge state that the loss is close to the middle between these two. As this is for nightly storage, the loss would distribute over two years (adding to other loss mechanisms). Whether an additional 12% degradation in two years is "too high" compared to 4% is up to everybody to decide.

[Smoother]

I remember someone one wrote here, (paraphrasing) 'if i have to keep my charge under 80% in order for my capacity not to drop to 80% in two years, What have I gained?"  In other words, if one self imposes an 80% charge max, then for all intents and purposes you are already operating at 80% capacity.  Since few of us keep wheels that long, I'd rather have my Volts up front, thank you very much.  In two years i'll have 80% forced on me anyway, and that doesn't even factor in age degradation; and by then I'll probably have something new and shiny under the Christmas tree.

(note, I rarely charge to 100%, I'm just not that anal about 80% or (insert your preferred percentage here),  Life's too short)