Question Does It Really Help to Only Charge a Laptop Battery Between ~40%-80%?

[Crag_Hack]

Hi I have a quick question, the title says it all. I did the relevant Google and found over here one guy said as quoted below regarding the question. So the question is what's worse, increased number of charge cycles or fuller charge/discharge cycles? Or is it more complicated than that?
Thanks!

This is a complex matter and different people give different answers, but basically they only one that can give a valid answer is the manufacturer of the specific laptop who has or should have the data for the specific battery behaviour.

It is true that batteries, especially the chemistry type used commonly in laptops do not like to be left fully charged for long periods. One has to assume that for this reason the manufacturer has set up the laptop in such a way that even if the user sees 100% charged, in reality the battery is not full. A buffer has been kept and the battery is at 90–95%. Doing the effort to use the laptop all the time between 40–80% and never go to 100% has two problems. One is that it is practically difficult to do all the time and the second is that you actually use battery cycles all the time. It will therefore age your battery faster.

Again, which exact usage pattern is the best for the battery is something only the manufacturer can answer. I assume however that the end result in terms of battery longevity is not hugely different.

Forget about all that and use your laptop the way it is most practical for your daily needs. The battery will not live for ever either way. My only suggestion would be if you leave the laptop unused for long periods (say a week or more) try to drive the battery SoG at 50% and shut it down. Do not leave it ON and connected to the power source. For the rest go as you please.

 

[Roland Of Gilead]

Hey there,

This is a bit of a conundrum, but essentially it boils down to the lithium ion batteries and their characteristics.

Let's say the battery has 500 + cycles of charge and drain. By limiting the max battery charge, in theory can extend the life of the battery as it would not reach the 500+ target. But, most batteries are designed for about 2 years before losing max capacity and degrading further.

Some OEM's have this set in the bios, or software. Personally I want the extra 20% battery run time when I'm running on battery, so I disable the option on my Dell in the bios. I guess if you're not gonna use the battery for a specific amount of hours per day, then charging to 80% won't be an issue. I think it's more a personal preference.

 

[Crag_Hack]

@Roland Of Gilead OK thanks, my usage case is almost never needing the 100% full charge. For me more of a desktop replacement for vacations. Also when you say 500 charge cycles, does limiting the max charge increase the number of charge cycles or does it only use a fraction of a charge cycle? How does that work?

 

[Eximo]

Charge cycles generally refer to full discharge and recharge cycles. There is no magic conversion to turn provisioned charges, or less than full charges to charge cycles.

You can approximate certain things though.

Say it is 500 full charge cycles. And you have a max flyable 100 Wh size battery. That gets you 50,000 watt hours. If the laptop averages 15Wh to run on battery, that gives 3,333 hours of run time. Which is approximately 1.66 years of 8 hours per day on battery. Now that doesn't make realistic sense since you aren't going to spend all that time on battery.

Staying away from the bottom and top end of batteries does increase their life, but to what degree depends on how much you draw and how fast you charge. 1C (C standing for capacity, being able to recharge the full capacity in an hour) is the top end usually for Lithium, and a lot of laptops can and do charge faster than that. 65W charger on a 65Wh battery (or thereabouts) is quite common. But you see many laptops with larger chargers so that you can run high end systems while not draining the battery so much.

 

[Crag_Hack]

@Eximo K I'm guessing the more you draw and faster your charge the worse for the battery lifespan?

hmmm... just used Dell Power Manager to restrict charging between 50% and 80% and it appears to be staying at 80% capacity when plugged in and not discharging at all. Is that bad for the battery? Is it better to let it drop to 50% then charge back to 80% and repeat?

 

[Eximo]

Correct.

That is kind of up to you. 50% would be preferable for long terms storage as mentioned previously. If 80% meets your needs for the occasions you do unplug then the battery should last longer.

 

[Crag_Hack]

@Eximo Returning to this thread after a brief hiatus... I think you misread the question. I almost never use my laptop without access to an AC outlet. The question is is it better to keep it plugged in all the time with smart charging on and thus the battery capacity stays at a constant level somewhere between 50% and 80% or is it better to charge it to 80%, let it discharge to 40%, recharge to 80%, and repeat as needed indefinitely. Thanks again!

Also it seems Dell Power Manager will keep the battery at whatever percentage capacity it's at when you plug it in if it's in the interval 40%-80%, and if it's below 40% it will charge it to 80% then keep it at 80% for however long it's plugged in.

 

[BFG-9000]

I'll suggest reading this. The short of it is charging only to 80% and never discharging below 20% will double the cycle life of the battery compared to 100% and 0%, so that Dell algorithm appears to be reasonable enough. But of course then you only get to use 60% of the battery capacity per cycle so the total energy you get out of it over its life is only about 20% more.

However it may be a good idea to occasionally charge to 100% to keep the cells from going out of balance. Apparently how the balancers work is when the 1st cell hits 4.2v, charging continues except for that cell where the current is diverted. This repeats as each cell reaches 4.2v until the last one does, when charging terminates. The result is all cells get balanced, but this process only works when charging to 100%.

Storage at 100% isn't recommended as at 25°C this means 20% permanent capacity loss per year. There doesn't appear to be much difference if storing between 40% and 60% charged with about 4% loss per year, but storing at 0% charge is probably just as damaging as storing at 100% (and easy to accidentally do unless you are monitoring frequently). This is with no cycles at all, so closest to your use case.

 

[Viking2121]

I mean the experts say so, I don't worry about it personally as I want my stuff to be fully charged when I need it, I don't want to leave with it and forgot I took it off charge to follow an experts advice and only have like less than 50% life or less. Kinda defeats the purpose of mobility in my opinion.

But I will take it off charge if I know im not gonna use it for a long time, I don't like leaving them on charge for days at a time, that isn't good for it, or leaving it dead for days at a time. My surface pro 4 I throw it on charge for a few hours than take it off, I don't use it much while im home.

If a laptop was my every day only rig, I'd try to get at least a full charge cycle on it a day if all your gonna do it leave it at home most of the time anyway, I don't see it being practical unplugging it over and over again after it gets to a point.

A battery I feel is gonna need to be replaced at least once at some point its life no matter how you take care of it. My Surface pro 4 I bought late 2015, still the OG battery, sits fully charged most of its life, I do take it off charge and kinda cycle the battery using in the garage or something from time to time, I can still get close to 4 hours on a charge watching youtube on it.

Everyone is different, Some people are willing to take the 20% hit to max charge, Im not one of them, I want the max I can get out of it, even cell phones, some people wont let their phones charge past 80%, I charge that sucker to 100% everytime, well my phone is a from 2018, I still get 2 to 3 days out of it, so Idk, if the the life of my battery weakens, I think I'll just buy a new phone, or laptop, be too slow for my needs anyway, Thats how I see it.