MacBook Battery
Posted on Nov 26 - 2023
I kept my MacBook charged for a year

In early October, I purchased a MacBook Air M2, 13", 16GB RAM, and 512GB SSD. Except for a couple of moments, the laptop was always connected to the power outlet for an entire year. Clamshell mode, external monitor, no software programs to manage the battery but only Apple’s optimized battery charging enabled.

This will be a brief summary of what is the biggest fear of every user who buys an Apple device with a battery:

“If I always keep the device charging, will the battery get ruined?”

In this case, I am speaking about my product and therefore only about the category of MacBooks.

 

 

Index

Table of contents

 

 

Warning

Mine is not an experiment in the true sense of the word. I haven’t conducted specific tests to check the health of the battery, nor do I have the indicated hardware and software to analyze in detail every component that revolves around the deterioration of a battery.

This is simply a personal experience that I want to share with anyone interested in this topic, avoiding endless discussions on the internet.

 

 

Why?

The choice between a desktop or a portable device depends on the user’s needs. For years, I used a Mac Mini and a MacBook Pro to keep my workflow linear. The Mac Mini allowed me to replace storage space where I kept most of my heavy projects and data, while the MacBook Pro allowed me to work on the go with good computing power.

In the end, however, maintaining two devices for the same purposes became somewhat unnecessary and costly. Software and hardware obsolescence, synchronization management with all apps, maintaining a correct flow, and other elements led me to have to maintain two devices rather than one.

With the advent of Apple Silicon with ARM architecture, things have completely changed. A MacBook can very well represent a desktop device with all the potential of a laptop. Maximum flexibility, excellent battery life, excellent performance, and above all portability.

So, I combined two devices into a single MacBook, simplifying my workflow and data management.

Being the first time, like many, I searched the internet for advice, suggestions, and experiences of people who always kept their MacBook charging; and, as always, there are far too many conflicting opinions. It ranges from those who have completely ruined the battery to those who have had no problem. There is no middle ground, only two extremes.

For this reason, I decided to try first-hand the performance of my device’s battery by always keeping it charging.

 

 

Lithium-ion

It should be noted that the battery of the MacBook and most of the devices we use are composed of lithium ions.

The first thing to keep in mind is that:

Lithium batteries lose their ability to store energy over time, regardless of device usage.

Logically that excessive use can lead to a faster loss of storage capacity, but it’s not the only factor that influences battery life. Many usually consider that the number of cycles a battery has undergone determines its health, but this is not the case.

For those unfamiliar with the concept of charge cycles, the Apple support page explains it simply:

“You complete one charge cycle when you’ve used (discharged) an amount that represents 100% of your battery’s capacity, but not necessarily all from one charge.

For instance, you might use 75% of your battery’s capacity one day, then recharge it fully overnight. If you use 25% the next day, you will have discharged a total of 100%, and the two days will add up to one charge cycle.”

 

 

Precautions

Some precautions can be kept in mind to avoid maximum deterioration of your device’s battery.

In particular:

  • Maintain the appropriate temperature
    Avoid exposing the device to extreme temperatures, both hot and cold. Li-ion batteries work best at moderate temperatures between 20°C and 25°C.

  • Avoid complete discharges
    Avoid completely discharging the battery before recharging it. Frequent complete discharges can accelerate the decay of capacity.

  • Use original or reliable chargers
    This is one of the points underestimated by many. Poor quality chargers can negatively affect the health of the battery or even lead to dangerous situations.

  • Charge moderately
    Use chargers that provide a moderately fast charge. Charging slowly can reduce stress on batteries.

  • Avoid intense use during charging
    Avoid using the device intensively during charging. Intensive use can generate heat and negatively affect the battery.

Taking these premises into account, we can move on to analyzing the data.

 

 

Initial Capacity

I purchased the MacBook in October 2022, received it towards the end of October, and from November 2nd, I started using it always connected to the power supply.

The software I used to keep track of the battery information is Coconut Battery Plus.

Coconut table showing the charge cycles, life, and maximum capacity of the battery from 2022-11-02 to 22-12-18.

As you can see, for the entire month of November, the life of the battery hovers around 101.4%.

This result should not raise concerns or oddities as several factors come into play:

  • Initial calibration errors
    Sometimes battery sensors can be slightly out of calibration and show incorrect values that are corrected with the use of the device over time.

  • Calculation algorithm
    The software that provides the battery status can use complex algorithms to estimate the overall health of the battery, taking into account various factors such as the number of charge/discharge cycles, temperature, etc.

    These algorithms can theoretically produce values above 100%, indicating superior health.

  • Redundancy in the nominal capacity
    The nominal capacity of a battery is established by the manufacturer, but the actual battery can occasionally slightly exceed this specification. In this case, the software might show a percentage above 100% to reflect this “extra capacity”.

  • Software updates
    In some cases, software updates can affect battery status readings.

  • Other factors.

This is demonstrated by the row of 2022-12-04 where it abruptly drops to 99.3%.

Now, pay attention to the reading of the Maximum Capacity column. The maximum capacity of the battery can be expressed in watt-hours (Wh) or milliampere-hours (mAh).

On the Apple website, the capacity is in watt-hours, and it is 52.6 Wh; while the capacity expressed by Coconut is in mAh, and it’s 4628 mAh.

Essentially:

Factory capacity declared by Apple (Wh) = 52.6 Wh
Current capacity expressed by Coconut (mAh) ≈ 4628 mAh


We use as three recharge cycles have already been carried out.

Considering that the voltage is more or less 11.39 V, we convert the current capacity of Coconut into Wh:

Capacity (Wh) = (Capacity (mAh) / 1000) x Voltage (V) ≈ 52.6 Wh


The lost capacity is trivially given by:

Lost capacity (Wh) = Capacity (Wh) - Current capacity (Wh)


So:

Lost capacity (Wh) = 52.6 Wh - 52.6 Wh ≈ 0 Wh


The lost capacity is zero*1, which means that the current capacity is still equal to the original capacity of 52.6 Wh. There has been no evident loss of capacity despite the three recharge cycles.

So we can consider the battery as new in its initial state.

Interesting to note is the fact that the maximum capacity decreases, showing that lithium-ion batteries lose their capacity over time.

*1 Obviously, the value is not exactly zero, but the difference is so small that we can overlook it and consider the value as zero.

 

 

Analysis

From November 2, 2022, to November 11, 2023, the MacBook was always connected to the power supply. My usage is not intense but is prolonged, meaning I use the MacBook every single day without any exception. Moreover, the MacBook was never turned off or restarted except to perform macOS updates.

The software used is mainly related to programming and development, from simple scripts to the compilation of complex projects. In addition, all the other elements constantly running in the background like Docker, databases, servers, etc. So we’re not talking about simple browsing or watching YouTube.

From this overview, we connect to the main table with all the information collected month after month.

Coconut table showing the charge cycles, life, and maximum capacity of the battery from 2022-11-02 to 22-12-18.

The table contains some redundant rows and unfortunately, the recording for the month of June is not present (so I will use the end of May row to represent the month of June; also because there are no radical changes in the number of cycles and battery health).

For simplicity, I summarize the data below:

DateCyclesHealthCapacity mAh
22-113101.44628
22-12399.34529
23-01499.44536
23-02499.34533
23-034100.44580
23-044101.64636
23-055101.34621
23-065102.14657
23-078101.44626
23-088101.34621
23-091299.14524
23-101398.74502
23-111894.94329


Even in this case, we must emphasize that we are not talking about specific software that analyzes all possible states of the battery, so situations where it seems that the battery over time becomes more capable in capacity are only related to the factors already mentioned earlier.

Based on these data, we can make some considerations by analyzing the table of cycles and that of maximum capacity.

 

 

Cycles

The first point to discuss is the presence of cycles, up to 18, of a device always connected to the power grid. In reality, it is not as strange as it seems, these cycles are due to various factors:

  • Apple’s Optimized battery charging
    Once the option is enabled, unfortunately, the battery percentage will not immediately drop towards 80%, but only after a few days keeping the MacBook always connected to the power outlet.

    Even on this option, there are many conflicting opinions on the necessary time for which macOS enables optimized battery charging, but in my case, keeping the MacBook always connected to the power outlet, I did not give it particular weight and I left the option always active.

  • Voltage drops or lack of current
    Over the the year they brought a reset of the optimized battery charging, so the battery was charged to 100% and then, after a couple of days, it returned to 80%.

  • Some outings
    That I did with the MacBook without electrical power.

Going into detail, Coconut provides a chart that shows the set of data on the average battery capacity based on charge cycles.

Battery capacity based on loadcycles by coconutBattery.

Ignoring the strange trend between 150 and 200 cycles, if we focus on the two black arrows, we can see how the capacity of my battery (oblique arrow pointing to the bright green line) is in the same set as those who have carried out an average of 80 recharge cycles (horizontal arrow).

Of course, this is just part of the data provided by this software, but it gives us an idea of how the battery behaves based on charge cycles.

In addition, I wanted to try using artificial intelligence to search and aggregate all the information at their disposal. In particular, I used Google’s Bard and OpenAI’s GPT; both subjected to the same question: “If the user has carried out 80 recharge cycles and the battery has an original capacity of 100%, the battery should be at about ?% of its capacity considering that the user uses his device mainly on battery rather than connecting it to an electrical outlet”.

Google’s Bard:

If the user has carried out 80 recharge cycles and the battery has an original capacity of 100%, the battery should be at about 92% of its capacity.


OpenAI’s GPT:

So, the battery should theoretically be around 90% of its original capacity.


Both Bard and GPT provided a value more or less close to my current value of 94% expressed by Coconut.

We can therefore highlight two things:

  1. Even if the number of cycles is low, it doesn’t mean that the battery has not deteriorated.

  2. In my case, despite the MacBook being mainly connected to the electrical network, the battery has followed a trend similar to the average use mainly on battery.

So, in this case, it’s not true that keeping the MacBook always charging leads to a greater loss of battery capacity.

 

 

Maximum Capacity

As mentioned at the beginning, the capacity of a battery tends to decrease, starting from 4628 mAh to 4329 mAh for a total rounded loss of 300 mAh.

We can again compare these values with some data provided by Coconut on battery capacity based on charge cycles.

Battery capacity over time by coconutBattery.

In this case, after a year, the maximum capacity of my battery is in the same range between 4600mAh and 4400mAh. There is indeed a difference between the trend of the battery (bright green) and the midpoint (light green) which is lower, but the difference is not so marked.

Even in this case, we could conclude that keeping the device always connected to the power supply has not led to a worse loss of battery capacity compared to those who use the MacBook on the go without keeping it constantly connected to the power supply.

 

 

Updates

The installation of updates is another parameter that can influence the battery. Different management, realignment, or stabilization of battery data can lead to radical changes in the collected data.

Taking into account the dates in the table below, you can see how the update to Sonoma increased the number of cycles even though the MacBook was always connected to the power grid.

DateVersion
2022-10-24Ventura 13.0
2023-09-26Sonoma 14.0
2023-10-25Sonoma 14.1
2023-11-07Sonoma 14.1.1


In the release notes of Sonoma 14.0, there is a section regarding other improvements that have been made, among which:

Battery health management updated on 13-inch MacBook Air with M2 chip to better optimize long term battery health.


This could be the reason why from Sonoma to today the number of cycles has increased faster compared to previous periods.

Among the possible causes could be that Apple’s optimized battery charging on Sonoma does not always keep the charge at 80% but performs mini cycles. In fact, I happened to see the battery percentage drop from 80% and reach percentages like 75%. Or, despite no change, the battery started charging up to 100% and then reached 80% in a few hours.

These are the only hypotheses that come to mind to explain this increase in cycles knowing that the MacBook has always been connected to the power grid.

 

 

Conclusions

Based on this small experience, the conclusion that could be drawn is that keeping the MacBook always charging does not lead to a greater loss of battery capacity compared to those who use the MacBook on the go or tend to take care of the battery by changing their way of using the device.

Essentially:

Use your product in the way that best suits you and not the other way around, it makes no sense to change your way of using a device to preserve it as much as possible.

I know that this conclusion may go against many people who have spent time and money to purchase a product like a MacBook, and it’s right that they try to preserve it as much as possible but it’s equally right not to obsessively rack your brains about the battery completely changing your own way of relating to a device.