Yes, it degrades the battery. Modern laptops (especially gaming ones) have the ability for the power to pass into the components directly instead of the battery when it’s fully charged, so the battery doesn’t degrade, most phones don’t have this capability (they can, but not worth putting it in).
Yes it will degrade. It’s not good for your battery to be at 0% or at 100% for an extended period of time. This is why some phones have a feature to only charge to 80-90% now).
Batteries can be damaged by overcharging them. Modern systems detect when a battery is full and stop charging.
Batteries can be damaged by the charging process. Charging them over and over every time they dip to 99% will damage them over time.
Batteries can be damaged by storing them at full charge. This is why batteries that you get on a new device in the mail are generally stored at 50%-80% charge.
Batteries can be damaged if they are not fully discharged from time to time, this is called battery memory. While it is less of a problem in modern batteries, it is still a concern.
All of these are happening when you keep your battery plugged in at 100%.
Lithium batteries like the ones in your phone or laptop store energy using a special kind of chemistry. Think of it like a stretchy spring: it likes being in the middle, not stretched or squished too much. That “middle” is around 50% charged.
Every time you charge it to 100% or drain it to 0%, you’re stretching or squishing that spring all the way, which slowly wears it out. Over time, it can’t hold as much energy as before.
That’s why modern devices (like iPhones and Macs) have smart charging. If they notice you always keep your device plugged in, they might stop charging at 60–80% to protect the battery. It’s like letting the spring rest in its comfy spot more often, so it lasts longer!
It’s going to depend on the exact device. My 3½ year-old MacBook Pro is plugged in 95% of the time and the battery life is still at 90%. There’s an option called “Optimize Battery Charging” that’s on by default.
Batteries drain slowly no matter whether they are being used or not.
Also think of a battery like a rubber band. The band is happiest at about 70% if you stretch it to 100% it feels a little over stretched one way, if you get it down to 0% it’s over stretched another way.
It’s ok to stretch to these numbers for a little while, but if you make them hold it too long then they get worn out and it’s not as stretchy as it used to be.
That’s what happen when you keep it charged at 100% it wears out your battery.
There’s a lot of answers here on the batteries themselves but I think answers generally overlook one important aspect.
Most, if not all, modern devices have very sophisticated battery management systems built in. They pretty much wouldn’t let you overcharge if left plugged in, slow down or stop the charge rate as it nears 100%. Monitors your usage and charge patterns and adapts how the battery charges when plugged in to compensate. Monitor and compensate for bad cells, etc.
Modern lithium ion based devices should last years without the end user having to worry about charging patterns or being constantly plugged in.
i have an msi laptop and i plug it in every time i use it bc it has a feature where it only charges the battery if it is less than 50% and stops charging once it reaches 60%. so the battery is always at 50-60% and remains unused when kept between this range. goodbye charging cycles. goodbye battery degradation.
Most modern phones can not bypass their battery when running plugged in, due to how their power-circuits are laid out, so there is degradation even when running off wired power. “Batter saver” modes only reduce the stress on the batter by reducing the peak voltage and thus degradation on the electrodes, but that doesn’t change the fact that the battery is still being drained and recharged while in use on plugged power.
That’s why most phones won’t be able to start if you were to remove the battery but connect to a charger. It’s really a shame for waste reduction (and some cool use cases for old phones), but apparently makes the devices cheaper and a smaller to make, plus adds some planned obsolescence so you all definitely have to buy a new phone every few years.
Putting many cycles into the battery (i.e. using it)
Apple has software that can stop charging the battery at 80%, and then bypass the battery entirely so your computer runs off the charger only and your battery isn’t being used but isn’t sitting at 100% either. But this system only turns on when it feels like it so it’s not that useful.
I remember that on the old Dell laptop I got for college in 2014, if you had it plugged into the wall and it hit 100% battery, it would switch to running purely on wall power with a notification that it was “running on AC power”. Why don’t devices do that nowadays? Is it a matter of the hardware needed to switch is too big or runs too hot to fit into modern smartphones?
This depends on the battery chemistry, a lot of what you’ll see written about this is based on old tech we dont use anymore. But for lithium batteries it goes like this:
Imagine your battery has lives, about 1000 – 5000 lives.
It loses a life every time the battery drops below 20% and charges over 80% .
Keeping it always between those or always outside of those will prolong the battery life.
This is in contrast to old battery chemistries like nickel hydride. They liked to be deep cycled and would get ruined by being kept full.
Either way batteries are consumerables, eventually it will die.
Charge controllers exist. They’re fairly cheap and easy to include on pretty much any device since they’re only comprised out of very simple electronics. They can control the charging rate or cut off charging completely even if the device is plugged in to protect the battery. They’ve become more commonplace in recent years but it’s not like they’re new. The simple reason why companies don’t just include them on any and all electronic devices is because it’s better for them in the long run if people frequently change their devices every few years rather than having a device that lasts a long time.
Here’s the copy/pasta of an article I wrote for ELI5 ten years ago:
I used to work on the battery charging logic for both server backup power supplies in data centers, and for cell phones. A few notes:
It’s bad for all batteries to deeply discharge them. Avoid this if you can.
It’s a little bad to charge a Li-Ion battery all the way, but if you don’t know how long it’s going to have to go without recharging it, it’s best to charge it to 100% up front rather than risk deep-discharging it later. Otherwise, your target is 80%.
In general, “recharge early, recharge often” is your best approach.
The charging logic in a laptop or cell phone is quite sophisticated. It knows to stop charging when the battery is full, and to shut down your device when it gets too low. It knows when to trickle-charge, and when to charge at full current.
Pretend you never heard of the “memory effect” for NiCad batteries. Unless you work with space satellites built in the 1970’s, it doesn’t exist for you. Trying to avoid the memory effect probably kills more NiCads than anything else. Anybody who thinks they’re seeing the memory effect is really just seeing a battery that doesn’t hold much charge any more.
For NiCads, fast charging is much better than trickle charging because trickle charging encourages the growth of dendrite crystals in the cell, which damage it. I dunno if this applies to other technologies.
Some people think that the number of discharge/recharge cycles matters, and thus it’s better to let a battery discharge all the way before recharging it, on the theory that one full cycle is better than two half cycles. Stop thinking that way. Two half cycles are much better than one full cycle, and the battery “cycle-counting” logic treats them as one cycle.
Fun fact: charging a Li-Ion battery the last 20% takes far more energy. We had a design for a portable battery charger that would only charge to 80% for this reason.
If I were to set the policies for charging systems, I would add the rule “If the device hasn’t been used in 24 hours and the battery is below 40%, shut the device down. If the device hasn’t been used in 48 hours, shut it down.” I work with cell phones and tablets for a living and have a shelf full of them. I really hate picking one up and realizing that it’s been off the charger for a week and drained its battery to zero in the meantime.
Lithium batteries are like goldilocks for how charged they are = not too much, not too little. Leaving a battery at 100% for a long time is not good for it, same with 0%. The closer to the extreme, the faster the degradation.
Also there is not hard rule for what is 0% or 100%, it is based on the voltage of the battery. One manufacturer may set 100% to be higher than another. Those batteries will hold more energy, but degrade faster.
TLDR: When keeping the battery at 0% for a long time, it damages it due to the electrons overpower the protons causing stress, on 100% the protons overpower the electrons, again, causing stress, at 50% as Thanos would say everything is perfectly balanced and no stress is present (theoretically), I keeo my laptop limited to 50% as it’s always plugged in and the battery is as good as new, the phone I limit to 80% unless I travel, keep in mind it’s good practice to let your device run down to 0% and then charge it back up to 100% and leave it there for a bit, to recalibrate the battery circuit.
Think of the battery as a balloon. If you keep it inflated fully for a long time and then deflate it, it will be loose and not go back to it’s original size. On the other hand, if you inflate it fully and deflate it fully immediately it will almost go back to what it was. Now, if you inflate it to 80% and deflate it to 20% and stay in that range you’ll always have a tight balloon and not cause much permanent damage.
We have an HP Laptop at work. Never left it’s charger since 2021. Now the battery only lasts about 40min at 80% brightness, about 1.5 at lowest. So yes, it degrades
Comments
Yes, it degrades the battery. Modern laptops (especially gaming ones) have the ability for the power to pass into the components directly instead of the battery when it’s fully charged, so the battery doesn’t degrade, most phones don’t have this capability (they can, but not worth putting it in).
Yes it will degrade. It’s not good for your battery to be at 0% or at 100% for an extended period of time. This is why some phones have a feature to only charge to 80-90% now).
Batteries can be damaged by overcharging them. Modern systems detect when a battery is full and stop charging.
Batteries can be damaged by the charging process. Charging them over and over every time they dip to 99% will damage them over time.
Batteries can be damaged by storing them at full charge. This is why batteries that you get on a new device in the mail are generally stored at 50%-80% charge.
Batteries can be damaged if they are not fully discharged from time to time, this is called battery memory. While it is less of a problem in modern batteries, it is still a concern.
All of these are happening when you keep your battery plugged in at 100%.
Lithium batteries like the ones in your phone or laptop store energy using a special kind of chemistry. Think of it like a stretchy spring: it likes being in the middle, not stretched or squished too much. That “middle” is around 50% charged.
Every time you charge it to 100% or drain it to 0%, you’re stretching or squishing that spring all the way, which slowly wears it out. Over time, it can’t hold as much energy as before.
That’s why modern devices (like iPhones and Macs) have smart charging. If they notice you always keep your device plugged in, they might stop charging at 60–80% to protect the battery. It’s like letting the spring rest in its comfy spot more often, so it lasts longer!
Batteries don’t like being fully charged and don’t like being hot, both things that happen when you leave something running plugged in all the time.
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Worse then leaving a device on the charger with 100% battery is unplugging it at 80% with the device left powered up and then discharging the battery.
It’s going to depend on the exact device. My 3½ year-old MacBook Pro is plugged in 95% of the time and the battery life is still at 90%. There’s an option called “Optimize Battery Charging” that’s on by default.
Batteries drain slowly no matter whether they are being used or not.
Also think of a battery like a rubber band. The band is happiest at about 70% if you stretch it to 100% it feels a little over stretched one way, if you get it down to 0% it’s over stretched another way.
It’s ok to stretch to these numbers for a little while, but if you make them hold it too long then they get worn out and it’s not as stretchy as it used to be.
That’s what happen when you keep it charged at 100% it wears out your battery.
There’s a lot of answers here on the batteries themselves but I think answers generally overlook one important aspect.
Most, if not all, modern devices have very sophisticated battery management systems built in. They pretty much wouldn’t let you overcharge if left plugged in, slow down or stop the charge rate as it nears 100%. Monitors your usage and charge patterns and adapts how the battery charges when plugged in to compensate. Monitor and compensate for bad cells, etc.
Modern lithium ion based devices should last years without the end user having to worry about charging patterns or being constantly plugged in.
I’ve replaced multiple buggered laptop batteries because they were left plugged in
i have an msi laptop and i plug it in every time i use it bc it has a feature where it only charges the battery if it is less than 50% and stops charging once it reaches 60%. so the battery is always at 50-60% and remains unused when kept between this range. goodbye charging cycles. goodbye battery degradation.
Most modern phones can not bypass their battery when running plugged in, due to how their power-circuits are laid out, so there is degradation even when running off wired power. “Batter saver” modes only reduce the stress on the batter by reducing the peak voltage and thus degradation on the electrodes, but that doesn’t change the fact that the battery is still being drained and recharged while in use on plugged power.
That’s why most phones won’t be able to start if you were to remove the battery but connect to a charger. It’s really a shame for waste reduction (and some cool use cases for old phones), but apparently makes the devices cheaper and a smaller to make, plus adds some planned obsolescence so you all definitely have to buy a new phone every few years.
The two main causes of battery degradation are:
Apple has software that can stop charging the battery at 80%, and then bypass the battery entirely so your computer runs off the charger only and your battery isn’t being used but isn’t sitting at 100% either. But this system only turns on when it feels like it so it’s not that useful.
No, really old devices could do that . Anything post 2010ish has better battery management.
I remember that on the old Dell laptop I got for college in 2014, if you had it plugged into the wall and it hit 100% battery, it would switch to running purely on wall power with a notification that it was “running on AC power”. Why don’t devices do that nowadays? Is it a matter of the hardware needed to switch is too big or runs too hot to fit into modern smartphones?
This depends on the battery chemistry, a lot of what you’ll see written about this is based on old tech we dont use anymore. But for lithium batteries it goes like this:
Imagine your battery has lives, about 1000 – 5000 lives.
It loses a life every time the battery drops below 20% and charges over 80% .
Keeping it always between those or always outside of those will prolong the battery life.
This is in contrast to old battery chemistries like nickel hydride. They liked to be deep cycled and would get ruined by being kept full.
Either way batteries are consumerables, eventually it will die.
Charge controllers exist. They’re fairly cheap and easy to include on pretty much any device since they’re only comprised out of very simple electronics. They can control the charging rate or cut off charging completely even if the device is plugged in to protect the battery. They’ve become more commonplace in recent years but it’s not like they’re new. The simple reason why companies don’t just include them on any and all electronic devices is because it’s better for them in the long run if people frequently change their devices every few years rather than having a device that lasts a long time.
Does anyone know how much or how little these answers apply to EV vehicles?
Here’s the copy/pasta of an article I wrote for ELI5 ten years ago:
I used to work on the battery charging logic for both server backup power supplies in data centers, and for cell phones. A few notes:
If I were to set the policies for charging systems, I would add the rule “If the device hasn’t been used in 24 hours and the battery is below 40%, shut the device down. If the device hasn’t been used in 48 hours, shut it down.” I work with cell phones and tablets for a living and have a shelf full of them. I really hate picking one up and realizing that it’s been off the charger for a week and drained its battery to zero in the meantime.
ETA: Wikipedia article on memory effect
tl;dr: recharge early, recharge often. Leave it on the charger whenever you can. The charging logic in the device will know what to do.
Lithium batteries are like goldilocks for how charged they are = not too much, not too little. Leaving a battery at 100% for a long time is not good for it, same with 0%. The closer to the extreme, the faster the degradation.
Also there is not hard rule for what is 0% or 100%, it is based on the voltage of the battery. One manufacturer may set 100% to be higher than another. Those batteries will hold more energy, but degrade faster.
TLDR: When keeping the battery at 0% for a long time, it damages it due to the electrons overpower the protons causing stress, on 100% the protons overpower the electrons, again, causing stress, at 50% as Thanos would say everything is perfectly balanced and no stress is present (theoretically), I keeo my laptop limited to 50% as it’s always plugged in and the battery is as good as new, the phone I limit to 80% unless I travel, keep in mind it’s good practice to let your device run down to 0% and then charge it back up to 100% and leave it there for a bit, to recalibrate the battery circuit.
Lenovo has a vantage program which allows you to stop charging the battery at 80 percent full.
Think of the battery as a balloon. If you keep it inflated fully for a long time and then deflate it, it will be loose and not go back to it’s original size. On the other hand, if you inflate it fully and deflate it fully immediately it will almost go back to what it was. Now, if you inflate it to 80% and deflate it to 20% and stay in that range you’ll always have a tight balloon and not cause much permanent damage.
We have an HP Laptop at work. Never left it’s charger since 2021. Now the battery only lasts about 40min at 80% brightness, about 1.5 at lowest. So yes, it degrades