Optimal charging for batteries

[niwrad]

Hello,

Looking at the programming cycle satiator battery, was wondering about the best way to charge a battery

1) Does fast charging hurt cycle life if done at a low enough battery voltage, or batteries should be slow charged regardless of current battery voltage

2) Which would be a better cycle for maximum battery life: A) 80-20% B) 70-10% C) 60-0%

 

[billvon]

1) The slower the better
2) 80-20. Don't take them to zero - a cheap Chinese BMS may then continue to discharge them slowly.

 

[dogman dan]

Agree with the above response. For max lifespan.

But if its a pain in the ass to charge like that, then do what is not a pain. And if you have a bms, then only a full charge will balance the pack properly. This will be seldom needed if you do 80-20, and a low discharge rate. But at some point, it will be worth it to balance the pack. To do that with a bms, charge full wait half an hour, ride around the block, and then charge full again, wait half an hour, giving the bms two chances to discharge any too charged cells. Then ride again asap to get back to 80% or less.

Its time at full, that is the real big deal on early wear out. So when you do go 100%, ride asap.

In the end, if you really use that thing, you get your moneys worth by using it conveniently as possible. If you seldom use it, then pain in the ass charging routines can be the way to go. The more you use it, the more you want that full capacity, even if it means 100-5% use routine. Just minimize the damage, by charging full just before the ride.

 

[wturber]

Agreed about PIA charging. I started out all motivated to optimize charging. But I've replaced about 80% of my driving with my e-bike. So solution has been to:

1) use an over-sized battery (1250 watt hr) that I'd only fully used on a fast 40+ mile ride. That allows me to ride quite a few miles before I'm compelled to charge it. This results in me normally having the battery well above minimum charge and well below maximum charge most of the time.

2) After a daily commute to work and back where I use up almost half the battery by riding fast, I do a 45 minute charge in prep for the next commute day. That way I can top off the charge in the morning while getting ready for work ... or not in case plans change. If not, the battery is charged at about 80% and I don't mind leaving it there. If so, I can get a full charge while I'm getting ready to leave and run that charge down very soon so that the battery doesn't stay fully charged.

3) My charger is installed as a semi-permanent part of the bike. Charging is a matter of plugging in and moving an anti-spark XT90 plug connection. So charging is very low fuss.

So the vast majority of the time, my battery sits at between about 55% and 80% full. So I always have about 20 miles or more of range sitting there at the ready and I can usually get my full 40+ (actually well over 50 if I ride moderately) quickly. And with the charger always with me, I can recharge at my destination or anywhere I can find a plug in the odd event that I need to charge up while away from home.

 

[MadRhino]

Round cells? Pouch cells? LiCo? Specs...
Funny that someone is asking questions about battery management but doesn't say what battery it is.

Here is my general point of view about LiCo
Either they are high C rate, or low. Low C rate must be treated like you can kill them anytime, and probably a good reason not to charge them full.

High C rate LiCo chemistry, pouch cells especially, can take a lot of abuse, and that is précisely the reason why we use them on ebikes. 80% charge is about their storage voltage and you might as well leave them in the fridge forever and put them in your will if you want them to last.

Their ennemy is temperature, and that is what we need to measure to know when they are suffering. You can rely on never charging them really, and never use their power, to make sure they are not heating. That is the method of the innocent who can't use a thermometer. As long as their température doesn't start to rise, you can charge at speed and limit way above their ratings, and discharge as much power as you need, yet they are going to beat their rated cycle spec by far.

Never discharge any of your cells lower than 3.7v (most BMS can't tell, because they monitor cells by parallel groups). Arrange your battery configuration and air flow, such as to keep them all cells at the same temp (BMS can't tell). Never store LiCo chemistry charged above storage voltage, and overnight is storage. Never store LiCo that is plugged on anything, and BMS is anything. Never leave LiCo charging unattended, and everything they are doing "to make them last" is in reality, a mean of avoiding this important rule. BMS and slow partial charging, are tricks that compensate for incompetence.

From a long time LiCo abuser who never set fire to any cell, despite almost never balancing them and always overcharging.

 

[niwrad]

thanks for the advice, i did look around and it wasn't clear if there was a threshold limit to current battery voltage state when fast charging. I know fast charging is more suitable for discharged batteries, but don't know if fast charging regularly, but limiting it to just the first 50% of a battery's voltage state would do harm.

Additionally on one video from Grin, they mentioned that the lowest possible voltage is best for batteries, so that's why I ask if 80-20 is better or worse than say 70-10, and no one else seems to confirm or deny what Grin stated. To be fair it's not clear if they stand behind it and most people generally want reserve battery life rather than falling all the way to 10% or less regularly

I'm asking cause Im interested in the grin cycle charger, as it seems to be a good way to maximize the life of my batteries, which I hope not to replace for the foreseeable future and it has ways to program bulk amp speed and the maximum voltage to charge batteries to.

also for reference, I'm looking at Grin's LiGo, which has a BMS that self balances all cells at partial voltages, adding convenience to partial charging cells

also - Grin stated that in their LiGo setup, each battery has their own bms circuit(switch? controller?), so parallel measurement isn't a hinderance in their case

 

[wturber]

Additionally on one video from Grin, they mentioned that the lowest possible voltage is best for batteries, so that's why I ask if 80-20 is better or worse than say 70-10, and no one else seems to confirm or deny what Grin stated. To be fair it's not clear if they stand behind it and most people generally want reserve battery life rather than falling all the way to 10% or less regularly

That doesn't sound right. An approximate 50% storage charge is generally recommended for Lithium. That suggests that the "lowest possible voltage" is not best. Can you provide a link to the video?

 

[niwrad]

That doesn't sound right. An approximate 50% storage charge is generally recommended for Lithium. That suggests that the "lowest possible voltage" is not best. Can you provide a link to the video?

https://youtu.be/IxB2j-egWcQ?t=1385

start at 23 minutes and 5 seconds.

This is posted under their website near the bottom of their video collection

For those who don't want to watch he said -paraphrasing here-

'No much evidence that 80-20 is the best. if Choice between 80 to 20 and 60-0, 60-0 is better'

 

[wturber]

He didn't say that "the lowest possible charge is best." He did say that he's seen no evidence that going below 20% to 0% causes any particular problems and he's saying 0-60% is better not because the lowest possible charge is better, but because 60% is less likely to cause harm than 80% and more likely to increase longevity. This is a further reinforcement of the standard of a 50% or so storage charge - which they mentioned quite a few times.

A 0% charge may not, in itself cause problems, but it set's you up for possible problems because it puts you right next to states of charge that can cause permanent damage - depending on what kind of BMS you are using and what your likelihood of discharging below 0% are. Keep in mind that a charge level of 0% isn't fully discharged. The battery voltage can drop lower. What 0% means is that the battery has been discharged to the lowest level allowed per the manufacturers spec. That usually means the battery has a voltage of between 2.5 and 3.3 volts depending on the particular cell.. And if you let a cell discharge below 0%, for instance letting the voltage drop below 2v or so, you definitely run a serious risk of causing permanent damage. I would never leave a battery with a BMS at a near zero charge level for anything more than a short period of time (like even overnight, for instance) for concern that the BMS might trickle discharge the battery to damaging levels as Justin mentioned earlier in the video.

Circling back to the higher charge levels, it seems like high charge levels are potentially bad mostly if the battery has to endure them for long periods of time. This is why I don't fully charge my batteries the night before I ride. Also, keep in mind that the wearing out of a battery is generally defined by a lack of being able to hold a full charge - which robs your of the capacity that you paid dearly for. If you only ever charge a battery 60% you are effectively robbing yourself of that capacity ahead of time. If you only needed that 60%, then maybe you've overspent on battery capacity? I guess it depends on what your typical and maximum range needs are.

I suggest reading this article.
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

 

[niwrad]

He didn't say that "the lowest possible charge is best." He did say that he's seen no evidence that going below 20% to 0% causes any particular problems and he's saying 0-60% is better not because the lowest possible charge is better, but because 60% is less likely to cause harm than 80% and more likely to increase longevity. This is a further reinforcement of the standard of a 50% or so storage charge - which they mentioned quite a few times.

Well saying 60% is better than 80% more or less means a lower voltage is better, and you agree that he said going below 20% isn't of itself any problem, so the point becomes moot, and more about how much capacity you'll want out of a given battery.

A 0% charge may not, in itself cause problems, but it set's you up for possible problems because it puts you right next to states of charge that can cause permanent damage - depending on what kind of BMS you are using and what your likelihood of discharging below 0% are. Keep in mind that a charge level of 0% isn't fully discharged. The battery voltage can drop lower. What 0% means is that the battery has been discharged to the lowest level allowed per the manufacturers spec. That usually means the battery has a voltage of between 2.5 and 3.3 volts depending on the particular cell.. And if you let a cell discharge below 0%, for instance letting the voltage drop below 2v or so, you definitely run a serious risk of causing permanent damage. I would never leave a battery with a BMS at a near zero charge level for anything more than a short period of time (like even overnight, for instance) for concern that the BMS might trickle discharge the battery to damaging levels as Justin mentioned earlier in the video.

Hopefully Grin stands behind their product & warranty for their LiGo and their in house BMS circuits, but if not the cycle analyst should be able to cut off battery draw at a desired voltage level. Additionally they even mentioned that their LiGo can go to "sleep" which draws only micro amps, suitable for storage and shipping.

Circling back to the higher charge levels, it seems like high charge levels are potentially bad mostly if the battery has to endure them for long periods of time. This is why I don't fully charge my batteries the night before I ride. Also, keep in mind that the wearing out of a battery is generally defined by a lack of being able to hold a full charge - which robs your of the capacity that you paid dearly for. If you only ever charge a battery 60% you are effectively robbing yourself of that capacity ahead of time. If you only needed that 60%, then maybe you've overspent on battery capacity? I guess it depends on what your typical and maximum range needs are.

Obviously it's sort of about 'freedom'. In this sense I have the freedom to go on longer rides. It's sort of the same reason why drag strips and muscle cars exist. Buying more capacity than necessary gives me freedom, and as an added bonus, there's potential for increased cycle life. Grin mentioned this to me while I was asking about their batteries and they recommend getting a large battery just for the cycle life, even though it costs more up front.

 

[Sunder]

Wish i had kept some of the scientific papers people have posted here over time. You're just going to have to take my word for it, or not as your choice.

The papers approached the problem from different angles, different chemisties etc, but two things always turned up consistently:

1. Total time at near full charge. Going up to 4.2v/cell always shortened both calendar and cycle life, but leaving it up there when not in use caused more relative loss than only charging it up to that before use.

2. Charge rate had a higher impact on cycle life than discharge rate, and this needed to be temperature controlled. A battery that accepted 2C without getting hot/wearing excessively at 25*C, had to be dropped to 1C at 0*C to get the same life, and at as little as -10*C a single full rate charge could knock 20% of [either] capacity or power delivery rate even after bring back to room temps. (I don't recall exact details, but I am sure nobody would tolerate either)

I think there was difference between 80-20 and 70-10, but the difference was trivial especially when compared to 100-40, or 60-0.

 

[niwrad]

Yes, I agree with your first point. This seems to be explicitly stated many times.

For second point, that looks true, it seem discharge rates for pretty much every battery has always been higher than charge rates for a given battery, and I was surprised that warmer temperatures allowed for faster charging, although I did experience this first hand while using iphones in the cold, so I should not have been surprised.

I find this second point interesting, as it tells me people are charging their batteries outside in the dead of winter for fear of fires in their house. Hopefully battery technology improves since I leave my laptop, iphone, ipad and all sorts of gadgets in the house on top of all sorts of flammable things!

In any case, I dont expect any disaster buying the LiGo batteries as they seem to be well protected.

However my original question(s) still remain unanswered, but it seems there's often a conservative answer
1. Is fast charging, even at very low discharge rates, poor for battery cycle life? Phrased another way, is ANY amount of fast charging at LOW voltages going to be bad, and should one always charge at say 1/3 of the C rating of a battery? Evidence doesn't seem to indicate if a threshold exists or not, or is the evidence is not very clear at least as far as I can tell.
1a. This is mostly to decide what kind of profile I should use and whether the Grin charger can provide the performance and convenience I'm looking for.

Another Canadian, Linus of LinusTechTips, states that fast charging is potentially helpful in real life situations for prolonging cycle life, as it allows users to sort of cycle between low and medium states of charging instead of going 100-0-100 as is typical in cell phone use.

2. So the range of cycling is not much of an effect as compared to the maximum voltage? So the actionable question is how much reserve I'd like to have after completing a given trip. I only ask this question directly due to what Justin stated in that video, but if it is negligible, I'm more than likely to do 80-20 cycles than 60-0 to save on headaches.

 

[Sunder]

In any case, I dont expect any disaster buying the LiGo batteries as they seem to be well protected.

However my original question(s) still remain unanswered, but it seems there's often a conservative answer
1. Is fast charging, even at very low discharge rates, poor for battery cycle life? Phrased another way, is ANY amount of fast charging at LOW voltages going to be bad, and should one always charge at say 1/3 of the C rating of a battery? Evidence doesn't seem to indicate if a threshold exists or not, or is the evidence is not very clear at least as far as I can tell.
1a. This is mostly to decide what kind of profile I should use and whether the Grin charger can provide the performance and convenience I'm looking for.

This was addressed in one of the studies as well. Again, unfortunately have not kept it.

They key outcome was that internal resistance is not identical over the entire state of charge range.

Where internal resistance was low, the rate of charge could be safely raised, but where the internal resistance was higher, raised rates of charging damaged the battery.

So if your battery is dead flat, you don't want to push high rates of charge into it. As it approaches fuller, you can safely push more into it - especially if you never intend on going above 80% SOC.

The common factor appears to be internal resistance. The higher it is (Whether it is caused by temperature or state of charge - or even battery design), the slower you need to charge.

Edit: Actually, I think I misread your question, in which case I can't really answer it, well, not any more than I already have: And that is, given that at -10*C, even a single high rate charge can permanently damage the battery, I suspect the same could happen for a high rate charge in the wrong part of the SOC curve, or for whatever other reason.

There must be a lot of research into this, given the main focus of electric cars is reducing the "km per hour of charging" metric, but I suspect given the commercial implications of being first to solve it, none of the companies sponsoring the research are giving it out to academia - or enthusiasts - for free.

 

[niwrad]

Interesting, the internal resistant is the highest at low states of charge? The way fast chargers work seem to contradict this, as they put in more charge at the beginning than the end, assuming it's not below their lowest nominal state of charge

 

[Sunder]

Is that done programmatically, or because of the way CCCV works? Once it hits constant voltage, of course the current falls.

Or are you talking lead acid smart chargers? The do it programmatically to avoid off-gassing.

 

[niwrad]

I see, I thought resistance of discharged batteries was low assuming they're not over discharged, but it's surprising to see that it's even high than the 100% state of charge. Although the 80% mark, which fast chargers often charge to, is where there's an inflection point.

 

[Sunder]

Yes. You can feel that curve on the discharge side too. Go full throttle when the battery is full, and the voltage might only sag 2-4v (on a well designed 48v system). Try to do the same when the battery is less than 50% and it might drop 10v to trigger off LVC, even though you still have 50% capacity left.

The other thing I haven't mentioned is that 3.93v is a "magic" number. Keeping the voltage any below that doesn't gain you any extra life. It came from an early US Army study. Googling for it doesn't find me the study, but it does show a lot of references to the magic figure.

So I'd say to keep it simple, overspec your battery, charge to 3.93v at the slowest rate you can tolerate normally, and have a second charge profile at half the manufacturer's recommended 25*C charge rate for emergencies in case you need to charge in the cold in a hurry for some reason.

 

[dogman dan]

Seems like you want a specific answer to a general question. You are on the right track with a satiator. I need to get me one. Ability to change your charger when your battery changes, is priceless. And as they age, they darn sure do change. Or you get another thing that's totally different.

And I'm particularly good at the general answer, not a battery engineer, or any kind of engineer.

But Mad Rhino hit the general answer perfect, If what you do heats up the cells much, stop it. And, if you can, without getting into the pain in the ass situation, don't make the cells warm unless you have to. Warm better than hot, and not warmer than room temp better. Stone cold, not so good, below 50f they don't wear out, but they do lose capacity till warmer weather returns.


So watch your battery. We cant say what's too fast for your battery, we have no idea what you will get. But if you can charge fast, and they don't gain any heat at all, I'd say its not too fast. But,,, if you really are after the maximum lifespan, then you would charge, and discharge, as slow as is convenient for you.

For example, remember I said don't store them any longer than you must, for your convenience of use. So lets say you charge overnight. put them on charge at 6 pm, and won't need them till 7 am. In this case, why would you need to fast charge? On the other hand, if you work a half day, you'd want them full again in 4 hours for the ride home.

If you NEED a really fast charge, then you need as high a c rate battery as possible. You can charge a 60c lithium cobalt cell much faster than a 2c lifepo4 cell.


What works fine for many though, is just something that will charge fast enough to finsih before they go to bed. Or perhaps, charge to 70% by then, and finish when they ride next.

I fell asleep with a battery on the charger in my garage. My wife woke me up, so I didn't die when the garage caught fire. Now that's pain in the ass charging.

 

[wturber]

What works fine for many though, is just something that will charge fast enough to finsih before they go to bed. Or perhaps, charge to 70% by then, and finish when they ride next.

Right. After digging through lots of battery info, that is what I settled on as a routine. I charge to around 39 volts when I get home and will top off to 41v or whatever I get in the time I get ready for work. I also overspec'd my battery for my 32 mile daily commute so that even when charging at a moderately fast 8 amp rate, the per cell charge was well below manufacturer standard charge rates. That had the side benefit that the battery could still get me one way on my commute even if I forgot to charge it.

Now that my commute is cut in half, my battery has way more capacity than I need for day to day riding. I really have no good reason other than balancing cells or for an occasional long ride to charge the batteries fully. I'll probably reset my voltage to a max charge voltage of 41v this weekend.