Does charging my MacBook Pro 24 hours a day kill the battery?

The short answer is no but it's more complicated than that. If you have optimized charging enabled and the laptop is continually plugged in it will typically hold the battery at 80% and trickle charge the battery. The laptop will charge to 100% when it thinks you are going to be on battery. For example, if you plug your laptop in at night and then unplug it and use it on battery. The laptop should figure out when you unplug the charger, then it will start charging the battery to 100% before you normally unplug it. That's the theory anyway. The issue is that when charging from 80% to 100% is what causes excessive wear on the battery.

If you search Lithium-ion charging, you'll discover that keeping the battery between 80-30% charge will double the life of the battery. Charging to 100% or down to zero degrades the battery. Depending on the battery, the number of battery cycles it should go through differs. I'm told the new M1 MacBook Pros should charge at least 3,000 cycles which is a long time and if you're under warranty Apple will replace the battery when it falls to 80% capacity.

What I do is use a $12 countdown timer switch that my charger is plugged into. When the battery level on my MBP drops to 50% then I put the charger on for 30 minutes. With my 65 watt USB-C charger that will typically get me up to 70-80% charge. The battery life on the new Apple silicon machines is phenomenal and by using the timer I minimize wear on the battery.

Since last October when the 2021 MBP's came out my battery is now showing 65 cycles and if I was plugging it in overnight I'd probably have over 300 cycles and Battery Health shows the battery hasn't lost any capacity. Certainly, if you don't have access to a charger you are likely forced to charge to 100% but if you have it plugged in then buy a timer switch and just charge it for a few minutes when the battery level drops. For me I don't use the Apple 140 watt charger as it charges so fast that it's hard to catch it before it hits 100%. The USB-C 65 watt charger is about $25 and half the size of the factory charger.

A good article on charging can be found at: **-409: Charging Lithium-ion - Battery University

No.

Your Mac's battery and its circuitry will protect your battery better than a user micromanaging the battery.

Of course you'll find exceptions, but my 2016 MBP has been "on the charger" pretty much 100% of it last 3-5 years of life. It's capacity is 89% and it's been there for slightly over two years.

Search this forum and the overwhelming response you see will be "No"

"Of course you'll find exceptions, but my 2016 MBP has been "on the charger" pretty much 100% of it last 3-5 years of life. It's capacity is 89% and it's been there for slightly over two years."

My 2021 16-Inch MBP Pro is 10 months old and my battery has 100% capacity. It hasn't lost one percent of battery life and is close to half the age of your battery at 89%. That seems to be a pretty good argument for the "user micromanaging the battery."

My cell phone is 5 years old and has lost 2% of its battery capacity by user micromanaging the battery charging.

Apple states: "With iOS 13 and later, Optimized Battery Charging is designed to reduce the wear on your battery and improve its lifespan by reducing the time your iPhone spends fully charged."

Fully charging your battery reduces the life of the battery as proven by your battery losing 11% of capacity in 2 years or about 1/2 of 1 percent per month while mine has lost zero in 10 months. Using your example, my battery should have lost about 2.5% of its capacity. Apple's Optimized Charging is to reduce the inevitable wear of the battery. I just take it one step further to extend the battery's life by a factor of 2 at least. Apple doesn't state that their optimized charging eliminates battery wear but only minimizes it and with the user further micromanaging the charging it can be extended even further. While I won't know if only charging my MBP to 80% works until a couple of years down the road but hopefully I can wait to replace the battery. My Lenovo laptop actually stops charging at 80% while plugged in and doesn't start to charge until the battery drops to 70%. Lenovo is the only one I know of which will allow you to set the charge start and stop points without special software.

lobsterghost1 wrote:

My MBP is plugged in to charge 24 hours a day. When I go to bed at night, I put it to sleep. The next day, it's not at 100%, it's at 80%. Mine doesn't go to 100%, unless I restart it or power it down and turn it back on.

When I first noticed that Optimized Charging was happening, it was literally allowing the charge level to drop while it was connected. And then later it charged it up to 100% the next day. It didn't seem like it was doing anything that would be helpful.

However, for the OP there isn't really anything all that bad about leaving it connected. It won't actually be charging the battery continuously, as that's a sure way to destroy a lithium-ion battery. It will stop charging at a set point and then wait until the battery charge level drops to a certain point before topping off the charge. The primarily power needs will typically be provided by the external power, but the battery could be needed for supplemental power, such as when the CPU is in overdrive.

LyleFromVegas wrote:

That's easy to solve, sell your MacBook and buy a Lenovo LOL. The Lenovo allows you to set the maximum charge level and the point that it starts to charge. So you can do something like set it for 60-80 and the battery will charge to 80 and then when it discharges to 60, it charges again.

Optimized charging keeps the battery at 80% until it thinks you are going to use it and then it charges to 100%. Unless you need 100% battery then you can manually keep it below 80% but if you have it plugged in then the computer is going to control the charging unless it's overridden. A simple countdown timer switch and you keep it plugged in all the time and just power up the charger to bring the battery up.

I've seen it on a Lenovo and other computers. I believe the battery settings are actually more a Windows feature than a manufacturer specific setting, and it's up to the manufacturer to enable it in their distribution. However, this is the way that nearly every electric vehicle manufacturer allows the power management to be set.

But as far as this goes, I think it's pretty minor in the scheme of things. For years, Apple has been emphasizing that accumulating charge-discharge cycles is the primary thing that reduces battery capacity over time. But they don't allow for the one thing that would boost battery longevity the most when connected to power (aka "desktop replacement") which is to restrict the charge range with a user-chosen maximum (and possibly minimum) charge level. Optimized Charging is a simplified way of sort of trying to achieve something similar. However, it doesn't really bother me what way Apple chooses to do it. It's neither better nor worse - just different. And in the cosmic scheme of things, replacing the battery is relatively cheap compared to a new computer. And with "desktop replacement" it's unlikely that someone will manage to deplete a battery from use. More likely it will be a matter of aging as a result of time.

However, the most important thing for the OP is to understand that leaving it connected to external power doesn't mean that the battery is being continuously charged. That's been the case for pretty much every computer battery for at least the last 2 decades. If it weren't the case, we'd probably be seeing more battery fires like we've seen with vaping devices and hoverboards using poor quality charging systems that do tend to overcharge.

I could be wrong here, but it was my understanding that keeping a Lion battery at 100% charge continuously, is not good for the overall health of the battery. I keep my MBP plugged in all the time (with optimized battery charging turned on) and it stays at 80% charge, which I understood to be a better charge level.

Keep in mind that when the laptop is plugged in, it's designed to drop to 80% until the Optimized Charging figures out when you use it on battery. As I've previously stated, charging the battery past 80% reduces its capacity over time and if you keep the battery below 80% you can double the life of the battery. That is Apple's attempt to extend the life of the battery. When you start unplugging the laptop, the circuitry tries to figure out when it is used on battery and will charge to 100% before that time.

For me it is simple to manage the battery. I look at the battery percentage and depending on where it's at, I'll press 15-Min, 30-Min, 1-Hour, 2-hours, etc. charging time button on the countdown timer. It can't get much simpler than that. I can spend that much time to double the life of my battery and it's a no brainer.

The Apple stated life of a battery is down to 80% capacity before they feel it's worn out. With laptops now requiring serious surgery to replace things like the battery, I want to push that off as long as I can because it means more expensive repairs. I can swap out the battery in Wifey's 2015 MacBook Air in about 15minutes for $50-$75 and so I don't care that she abuses the battery but my $3,000 MBP is another story.

lobsterghost1 wrote:

I could be wrong here, but it was my understanding that keeping a Lion battery at 100% charge continuously, is not good for the overall health of the battery. I keep my MBP plugged in all the time (with optimized battery charging turned on) and it stays at 80% charge, which I understood to be a better charge level.

I don't particularly like the way Apple is implementing Optimized Charging on Macs. It's certainly a different environment than iPhones, where they pretty much force the charge level to drop. Holding off on when it charges up to 100% (such as with iPhones) is different than purposely cutting off external power use in order to allow the battery to drop to 80%.

The ideal would be a setting that limits the charge level to 80% at all times unless the user chooses to change it.

Enough senior, more knowledgable MBP members have suggested I don't need to micromanage charging and I've decided to just keep optimized charging on and not worry about, all the while keeping it on the mains all the time. It does take a few days to adjust to the 80% level. When I click on the battery charge at the top, it says "Charging on Hold, Battery Rarely Used."

LyleFromVegas wrote:

I realize that but Optimized Charging is similar across the types of devices and it's the first link that popped up when I searched for it. The issues with charging a Lithium-Ion battery are the same across the board in a cell phone, tablet, or laptop.

Not exactly. Size matters. A larger device can justify the use of a larger battery and slightly less use of the complete charge range. Theoretically it would be possible to double the nominal charge range of a typical mobile phone battery by using up more of it. Only that might reduce the number of cycles to bout 25-50. Less of the range can be used and bring up the number of cycles. There's a reason why iPads and Macs are rated for 1000 cycles while iPhones are 500.

Granted it's a huge pain to try and micromanage it without automation. I personally just leave mine plugged in most of the time unless I need the portability. If there were a setting to automate it (as there are with some Windows computers) I would choose it. I've personally chosen to turn off Optimized Charging because it's literally allowed the battery to drop to 80% while plugged in, which seems rather counterproductive to me to accumulate a partial cycle.

That's easy to solve, sell your MacBook and buy a Lenovo LOL. The Lenovo allows you to set the maximum charge level and the point that it starts to charge. So you can do something like set it for 60-80 and the battery will charge to 80 and then when it discharges to 60, it charges again.

Optimized charging keeps the battery at 80% until it thinks you are going to use it and then it charges to 100%. Unless you need 100% battery then you can manually keep it below 80% but if you have it plugged in then the computer is going to control the charging unless it's overridden. A simple countdown timer switch and you keep it plugged in all the time and just power up the charger to bring the battery up.

I've got an Asus and an HP Laptop running Windows 10 and they don't have a power management system that I know of. The Lenovo is a "business" machine and I think better made. The touch pads on most Windows machines suck and the Lenovo is the first one running Windows that actually works but none work like a Mac touchpad. Work gave me a Lenovo and I fell in love with the keyboard and touchpad. I found a used T450S for $300 and after investing about $300 in a new battery and SSD, it's a great machine. Some of the apps I have to use are available under Windows only which has kept me tied to a Windows machine. My new 16-Inch 2021 MBP now has Parallels and Windows 11 so I'm seeing if I can move all my Windows apps to the Mac and will ditch my remaining Windows laptops. Battery life on Apple Silicon is unbelievable.

I use my MBP mainly on battery but only charge it for the minimum time to bring it up to between 70-80% charge. There is a good article at the Battery University on maximizing battery life at https://batteryuniversity.com/article/**-808-how-to-prolong-lithium-based-batteries

Apple charges $199 plus tax in the US for a MacBook Pro battery service. I personally wouldn't trust an aftermarket battery. There have been too many reports of variable quality.

However, Optimized Charging on a Mac seems to me like a solution in search of a problem, which is why I turned it off. I couldn't figure out why it was allowing the charge level to drop to 80%, only to charge it back to 100% the next day. That's accumulating a fifth of a cycle daily that doesn't need to happen. What I would like is a real programmable setting where it only charges to 70/80/90% and stops there unless I want to charge it up to 100% and minimizes cycle accumulation. This is something that other battery powered devices can do - especially electric vehicles, and it's not particularly difficult to understand. However, EVs don't work where they're connected power in, although who knows with new technology such as wireless roadway power.

I don't want to be there monitoring the battery. Automating it is perfect because it would provide power and minimize the use the battery.

My MBP is plugged in to charge 24 hours a day. When I go to bed at night, I put it to sleep. The next day, it's not at 100%, it's at 80%. Mine doesn't go to 100%, unless I restart it or power it down and turn it back on.

You're in the MacBook community.

"Apple states: "With iOS 13 and later, Optimized Battery Charging is designed to reduce the wear on your battery and improve its lifespan by reducing the time your iPhone spends fully charged."

iOS is for iPads and iPhones

macOS is for Mac with the latest being 12.4