Is better to charge the battery only to 80%?

sisachosudo

10 mW
Joined
Dec 13, 2016
Messages
22
Hello all,

I just got a Stromer e-bike and after reading all the advice on how to keep a healthy battery, I have one question.

The bike comes with its charger (also branded Stromer) and during the charging process, you can see a progressing bar from X% until 100%.
I have read that in order to extend your battery life, is better to use from 20% to 80% of the energy stored in it. Do not fully charge or discharge the battery.
Does it mean that I should disconnect the charger when the battery reaches 80%?

I read somewhere that Stromer charger does not fully charge the battery but during the last 10% of the process is only balancing the cells. Not sure about it.
Does somebody know what would be the best way to do it? I only use 20% of the full capacity each day.

Thank you all!
 
If you only use 20% of the capacity, for longest life, only charge to 60%.
The battery will probably outlast your interest in the bike itself with your use case if you do that :)
Lithium batteries seem to live the longest, the longer you keep them to the middle of their state of charge. NASA found this out eons ago - i wish i still had the paper they produced about it.

Maybe give it a full balance once a year, but never leave it fully charged. The 100% charge should happen before a nice long luxury ride. :)
 
The paper you're talking about isn't quite right behavior for modern electrolytes with stabilization additives and modern active material passivity, but useful to show the concepts.

neptronix said:
If you only use 20% of the capacity, for longest life, only charge to 60%.
The battery will probably outlast your interest in the bike itself with your use case if you do that :)
Lithium batteries seem to live the longest, the longer you keep them to the middle of their state of charge. NASA found this out eons ago - i wish i still had the paper they produced about it.

Maybe give it a full balance once a year, but never leave it fully charged. The 100% charge should happen before a nice long luxury ride. :)
 
Yeah, it was an old paper. Maybe done in the late 2000's?

What is true today? i imagine it's still correct.
 
Maybe this is the one you are referring to...

https://www.google.com/url?sa=t&sou...FjAAegQIBRAB&usg=AOvVaw1lJieF0Nq3JpcRp3DTzTjV

From NASA in 2009.

It reads as follows:
"Capacity is adversely affected by high storage temperatures, high state-of-charge during storage, higher discharge rates, low temperature during charging, the stand time between charge and discharge, and operation at temperatures either lower or higher than the cell optimum temperature."

I understand that (in a perfect world) we should storage our batteries in a warm place, not over (let's say) 80% of charge, ride gentle (to avoid high discharge rates) and re-charge at room temperature.

On the other hand, the paper also says that...
"Cycle Life:
The number of charge/discharge cycles that have been performed by the battery affects both the voltage and capacity of the battery. As a battery is cycled, lower voltages and less capacity are available on discharge. These impacts are greater at more severe discharge conditions."

Does this last paragraph refers to full charge/discharge cycles?

Maybe I got lost in translation here.
If you believe that even having a large battery is better to charge a bit every day to keep it in the range of 20 to 60%... I'll do so.

I fully trust you :mrgreen:
 
"Cycle life" refers to full cycles. Not only do partial charge-discharge cycles count only partially against rated life in cycles, but keeping the state of charge (SOC) in the middle of the range seems to extend the rated life as well. So if you can get 500 full cycles from a lithium battery (not usually likely), you can get a total of more than 500 cycles in total when partial cycles are added up. This is because being in the middle of the SOC range is less stressful on the cells than being forced to their extremes regularly.
 
What I don't fully understand is why the battery or ebike sellers don't give that same advice to the buyers.
I am sure that plenty of them recharge their packs when is close to the min.

Even today at work, one colleague was proudly speaking about his long range battery saying that he only needs to connect it to the wall every 5 or 6 rides to the office.
I am sure that if he knew, he would not mind plugging it 45min after every ride.
 
LeftieBiker said:
"Cycle life" refers to full cycles. Not only do partial charge-discharge cycles count only partially against rated life in cycles, but keeping the state of charge (SOC) in the middle of the range seems to extend the rated life as well. So if you can get 500 full cycles from a lithium battery (not usually likely), you can get a total of more than 500 cycles in total when partial cycles are added up. This is because being in the middle of the SOC range is less stressful on the cells than being forced to their extremes regularly.

I understand, thanks.
I guess there isn't a negative effect linked to charge it a bit every time you ride. If so I don't mind plugging my battery for a while every night (20% of full capacity is used every day).

Thanks for your help.
 
sisachosudo said:
What I don't fully understand is why the battery or ebike sellers don't give that same advice to the buyers.
I am sure that plenty of them recharge their packs when is close to the min.

Even today at work, one colleague was proudly speaking about his long range battery saying that he only needs to connect it to the wall every 5 or 6 rides to the office.
I am sure that if he knew, he would not mind plugging it 45min after every ride.

Simple answer: They sell batteries. It's better for them if you don't know how to avoid buying batteries.

Less cynical answer: The vast majority of people selling these things have little or no idea how they actually work. At least not to the level of knowledge you will find on this forum.
 
sisachosudo said:
What I don't fully understand is why the battery or ebike sellers don't give that same advice to the buyers.

Mostly because they have no idea.

But even if they did, they wouldn't promote it, because it wouldn't make them as much money selling you a new battery when your old one dies.
 
The other reason that good battery practices aren't promoted is that they result in much shorter range or runtime than does full cycling. Treat your cell phone battery well and you get about half the runtime out of it - or more accurately, you are not using more than half of what is available. This can result in consumer dissatisfaction, and people switching brands for no good reason - they think it's a flaw with the one battery whose reps tried to tell them how to treat it right.

As for charging after every use, as long as it doesn't bring the SOC too high (roughly above 70%) and the battery isn't hot when charged, that is the way to go. It's pretty much what I do with my e-bikes and my Leaf: they rarely see a full charge, and never see a SOC below 20% (gods willing!). Most of us do a 100% balancing charge at least occasionally, although it isn't really clear that this benefits the battery as much as it satisfies our sense of order and balance. ;)
 
amberwolf said:
sisachosudo said:
What I don't fully understand is why the battery or ebike sellers don't give that same advice to the buyers.

Mostly because they have no idea.

But even if they did, they wouldn't promote it, because it wouldn't make them as much money selling you a new battery when your old one dies.
Jeebus all sellers aren’t sharks leaving customers in the dark to sell more. Often the new kit builder is overwhelmed by all the new information. Eventually we are able to take on more, but there’s no conspiracy.
 
BTW way treated my EM3ev first battery like shit. The mrs will do her 5th season in 2019. She just plugs it in to the 2A crap $20 charger.
 
With my smaller (<1kWh) packs, I find the utility of having my whole range available, and not being faced with running the pack all the way down, outweighs the potential deterioration from keeping the thing charged all the way up.

With my bigger pack, I still charge up to 4.2V/cell because I use a cheap charger. But I'm far more likely to wait later to recharge, because I know I'll have enough operating range anyway.
 
With my smaller (<1kWh) packs, I find the utility of having my whole range available, and not being faced with running the pack all the way down, outweighs the potential deterioration from keeping the thing charged all the way up.

The amount of time a pack spends at 100% is important, especially in warmer weather. If you time the charge so it ends not long before using the pack, it causes little or no harm. Letting it sit at 100% for days, though, can cause significant degradation, especially in warmer weather.
 
For what it's worth, I've sat there patiently explaining to new ebike users all about the charging, and how lithium doesn't like going real low, don't leave around fully charged etc... And had them come back saying I've been running the battery all the way down to dead before charging it and leaving it charged before going on vacation.... just like you said to!
 
From what I understand about li battery, it's a purely chemical problem: over time lithium oxide dendrites form over the electrode increasing its resistance which effectively decreases the battery's capacity. The higher the charge, the faster the reaction with a noticeable threshold around 4.2V - that's why it has been adopted as industry standard for those who want max. capacity. Other factors like temperature also play a crucial role, as higher temp = faster chemical reaction. Various tests have shown that the dendrite formation is very slow at 4.05 V, and quasi null at 3.92V (see batteryuniverstity.com So yes, it makes sense to charge only to 80%, but you end up loosing the main advantage of li batteries, which is a high power density, so I wouldn't get too fixed about it. You ought to strike a good balance between capacity and life cycles, so like many others, what I do is I charge the battery only when actually using the bike. This is really easy to do even with a cheapo charger when using a sonoff relay to schedule your battery charging time. But when I charge it, I need max. capacity, so I go all the way to 4.2V... knowing that this will ultimately end up killing my battery.
Nevertheless, If you build your battery pack yourself, changing cells is a few hours job well worth the little range addition, especially if you have a long commute trip. Now stromer is known for its very high pricepoint (waaaaay out for a simple tdcm DD motor with a fancy app, if you ask me), so if you don't want to void your warranty, I guess you have no choice but to adopt a gentle battery charge policy.
 
I do a load and go...similar to what the rocket industry does.... I'll charge to about 52v on my 48v pack and then load up in the am to around 54v right before I leave and just take it off the charger and directly onto the bike and I'm off...seems to be working well for me.
 
Thank me later:
https://endless-sphere.com/forums/viewtopic.php?t=86777

Matador
 
Thank you all. There is so much information about lithium batteries on the internet that it can be overwhelming sometimes. I am always looking for papers from official or reliable sources.

One question...
After my commute, I take my battery with me either to the office or home so it can stay cool and safe. I am doing it because I read that it is better to keep it at "room temperature" but I am hesitating now.
The bike is stored either at the bike room in the office which is kind of outdoors and this time of the year around 0-5 degrees Celsius (32°F) or when at home, in my garage which is around 10-15° Celsius (60°F).

According to your comments and links, I can see that colder is better for lithium batteries storage. I guess I could profit even more if I leave the pack attached to the bike at lower temperatures.
Of course, it would mean that when I am bike on the bike after work I will start riding the bike with the battery at 0-5°C.
Not sure what is the best option.

Quoting Jeff Dahn from this great article by the user "spinningmagnets", keeping a lithium battery in the fridge would extend their life time.

How do you extend the life of your battery in your phone or computer?
Keep it as cool as possible at all times, put it in the fridge at night. No, but I’m serious. If you keep any battery as cold as possible, it will last longer. So any, any lithium-ion cell, keep it in the fridge when you’re not using it, it will last longer. If you don’t charge 100%, that will help, but temperature is a bad actor.

https://www.electricbike.com/how-to-make-lithium-battery-last/

What do you think? Would you leave it or take the pack with you.

Thank you very much.
 
According to your comments and links, I can see that colder is better for lithium batteries storage. I guess I could profit even more if I leave the pack attached to the bike at lower temperatures.
Of course, it would mean that when I am bike on the bike after work I will start riding the bike with the battery at 0-5°C.
Not sure what is the best option.

60F is a good storage temp. Down near freezing not so much - especially if you plan to charge the pack. Charging a Chinese LiPo pack chilled to below 32F/0C can be downright dangerous, and I don't imagine that charging one not far above freezing is good for it either. Other chemistries are a bit more forgiving (My Leaf doesn't mind being charged at low temps - it's high temps that bother it) but if you want to treat it safely and want to be able to charge it without undo fear, try to store it above 40F (or Celsius equivalent) and below 80F
 
Running a cold battery provides greatly reduced performance, usable capacity and lifespan.
Long term only, store battery at cold (~ 40ºF) and <50% capacity.

Charge and use battery at ~ 70ºF, recommended.
(85ºF battery discharge demonstrates noticeable improvement, but much higher discharge temperature is deemed "damaging")

"Optimal" 80% battery cycling looks to be in the 5-85% - 10-90% range.
"Full" and "deep" charges\discharges have long and nearly universally been labeled as "detrimental to long life".

Loss of usable capacity a waste ... worry?
10Ah $100 battery 0-100% use = 1 year 250 cycles (optimistic estimate)
12.5Ah $125 battery 5-85% use = 3 year 750 cycles. (reasonable estimate)

Using 100% capacity greatly damages single cell or bank of non-optimal capacity, (causing premature pack failure), while 80% use provides great safety buffer for slight variance, at "full" or "empty", in cells resulting in more even, stable, deterioration.

Scheduled balancing and\or bank voltage monitoring highly recommended!
 
I worry about the humidity in my fridge. SO it's to a dehumidified basement around 50F in the winter and 65 in the summer. As good as I can do. Aug 2014 battery still making me happy.
 
Or large ziplock bag?
 
Sure, just like you, come up with a practical solution. Doh!
 
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