MacLenz
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The short answer
Keep the charge in the middle of its range when you can. For most desk work that means leaving the Mac plugged in with the charge held at 80%, which macOS can do for you. Avoid long stays at 100%, avoid running down to 0%, and keep the machine cool, because heat makes every one of these habits worse.
What each habit does to the battery
Leaving the charger connected sounds like it should be harmless, and in one respect it is. The charging circuit stops pushing current into the cells once they are full, so the battery is not overcharged. A top-up only returns when the cell voltage drifts down by a set amount, according to Battery University, a reference site run by the battery-testing company Cadex.
What the habit does do is park the cells at their highest voltage for days and weeks at a time. The battery is full, and it stays full.
Running the battery down first does the opposite. Each day you take the pack close to empty and fill it again, so every charge cycle is a deep one and the cells spend part of their time at the low end of their range.
One working day of battery level, four habits
The two habits stress different parts of the cell, which is why neither is the clear winner. The useful questions are how long the battery sits at each end of its range, and how warm it is while it does.
What a charge cycle really is
Apple defines a charge cycle as using all of the battery's power, though not necessarily in one go. Use half of the charge today, recharge fully, and do the same tomorrow, and that adds up to one cycle, not two.
Half today and half tomorrow is one cycle
So the cycle count measures how much energy you have taken out of the battery, in units of one full battery. Plugging in at lunch does not use up a cycle. It only means the next cycle starts higher. You can read the count in System Information, under Power.
The count treats every cycle as equal. The chemistry does not, as the next sections show.
Why lithium-ion cells wear out
A lithium-ion cell moves lithium ions between a graphite anode and a metal-oxide cathode. Charging pushes ions into the graphite and discharging sends them back. Capacity falls because some of that lithium stops taking part, and three processes do most of the damage, according to Battery University.
The first is a film that grows on the anode, called the solid electrolyte interface. It forms from lithium and electrolyte, keeps thickening as the cell ages, and the lithium locked inside it is gone for good. The second happens at the cathode. Above about 4.10 volts per cell, especially when warm, the electrolyte oxidises on the cathode surface, and the longer a cell sits at high voltage the faster this goes. The third is lithium plating. Charging fast can deposit metallic lithium on the anode instead of tucking it into the graphite, and that lithium is lost as well.
Three ways a lithium-ion cell loses capacity
A film forms on the anode from lithium and electrolyte. It keeps thickening as the cell ages, and the lithium locked inside it is gone for good.
Above about 4.10 volts per cell, especially when warm, the electrolyte oxidises on the surface of the cathode. The longer a cell sits at high voltage, the faster this goes.
Charging fast can deposit metallic lithium on the anode instead of tucking it into the graphite. That lithium is lost as well.
A battery's chemical age results from a complex combination of factors, including temperature history and charging pattern.Apple Support, on Optimized Battery Charging
Peak voltage is the lever you can pull. Battery University gives two rules of thumb. Every 0.10 volt taken off the peak charge voltage is said to double the cycle life. And a cell charged to 4.20 volts typically delivers 300 to 500 cycles, against 600 to 1,000 when it is charged to only 4.10 volts. A lower top charge gives you less capacity on each charge and a longer-lived cell in return. A charge limit makes the same trade.
Heat and a full battery
Battery University publishes estimates of the capacity a cell keeps after a year in storage. Two things stand out in the figure below. A full cell loses far more than a half-full one at every temperature, and heat makes both worse. At 25 °C a cell stored at 100% charge keeps about 80% of its capacity after a year, while one stored at 40% keeps about 96%. At 40 °C those numbers fall to 65% and 85%.
Capacity left after a year in storage
A Mac that is plugged in, full, and working hard in a warm room is the hardest case for the cells, because the full charge and the heat arrive together. Battery University's summary is that high temperature combined with a long stay at full charge can be more stressful than cycling.
Why shallow cycles last longer
Battery University also lists how many cycles a cell gives at different depths of discharge. For NMC cells, a cycle that runs from full to empty gets about 300 cycles. Cycles that use only 40% of the capacity get about 1,000, and cycles of 10% get about 6,000.
Multiply the cycles by the depth and you get the total energy the cell hands over in its life, counted in full charges. In the figure that total climbs from 300 full charges at 100% depth to 600 at 10% depth. The same cell gives you about twice the energy over its life when you take it in small sips.
Energy a cell delivers over its life, by cycle depth
Two cautions apply. These are lab figures for NMC cells, and Apple's own rating for its packs is 1,000 cycles to 80%, so the absolute numbers will differ. And the table says nothing about how long the cell rests at each end of its range. It shows a direction: small, frequent top-ups are gentler than deep swings.
The habits side by side
Plugged in all day, no limit
- Time at 100%
- Most of the day
- Depth of each cycle
- Very shallow
- What it costs you
- Nothing today. The cells age faster than they need to, most of all in a warm room.
Run it down, then recharge
- Time at 100%
- Short
- Depth of each cycle
- Deep, close to 100% every time
- What it costs you
- You use the whole battery, and each cycle takes the most from the cell.
Plugged in, charge held at 80%
- Time at 100%
- Almost none
- Depth of each cycle
- Very shallow
- What it costs you
- About 20% less battery when you unplug. One setting.
Mixed: unplug when full, plug in before it is low
- Time at 100%
- Low
- Depth of each cycle
- Moderate
- What it costs you
- You have to remember.
The last two look best on every measure the chemistry cares about. The first is the easiest and keeps the cells at their highest voltage. The second uses up cycle life fastest for the energy you draw.
If the choice is only between the first two, the first wears the battery through time at high voltage and the second through deep cycles. Which one costs more depends on how warm the Mac runs. In a warm room, with the Mac working hard while full, the first loses more.
What to do on your Mac
The two settings, in short
Turn on Optimized Battery Charging
It lives in Battery settings. It learns your daily routine and delays charging past 80% when it expects the Mac to stay connected for a long time, and it aims to reach a full charge before you usually unplug. It needs macOS Big Sur 11 or later.
Set a Charge Limit if your Mac supports it
On an Apple silicon Mac with macOS Tahoe 26.4 or later, open System Settings, click Battery, click the info button next to Charging, and choose a limit between 80% and 100%. Apple says the Mac charges to within a few percentage points of the limit and then stops. If the Mac lives on a desk, 80% is the setting the chemistry favours.
Charge to full before a trip
Choose Charge to Full Now from the battery menu before a trip, or a day away from a socket. Both features can be overridden that way. Apple also says the Mac will occasionally charge to 100% on its own to keep its charge estimate accurate, so an odd full charge is nothing to worry about.
Keep the Mac cool
Apple's range is 10 to 35 °C ambient. Leave room around the Mac so it can shed heat, especially while it charges and works at the same time.
Do not run it to 0% on purpose
Do not leave it flat for weeks, either. Apple warns that a battery stored fully discharged can fall into a deep discharge state and be unable to hold a charge. For long storage Apple recommends about 50%.
Skip the monthly calibration drain
Lithium-ion has no memory effect, and Battery University says the cells do not need periodic full discharges.
Questions people ask
Will leaving it plugged in overcharge the battery?
No. The charging circuit stops when the cells are full and adds a top-up only when the voltage drops. What staying plugged in costs is time at full voltage, which is why a limit helps.
Is it worth giving up 20% of the battery?
That depends on how you work. At a desk you give up nothing you were using, and when you travel you can override the limit. If you spend most days away from a charger, the limit costs you real runtime and the gain is smaller, so leave it at 100%.
My battery health already says 85%. Is it too late?
No, though capacity that has gone does not come back. Wear slows when the stress drops. Apple's design target is 80% at the rated cycle count, so a number in the 80s on a Mac that is a few years old is where the rating puts it.
Where the numbers come from
- Apple SupportAbout Optimized Battery Charging and Charge Limit on Mac
- Apple SupportDetermine battery cycle count for Mac laptops
- AppleMaximizing battery performance
- Apple SupportIf your Mac battery won't charge completely
- Battery UniversityBU-808: How to prolong lithium-based batteries
- Battery UniversityBU-808b: What causes Li-ion to die
Written by Aslam Sarfraz, an independent developer, from the sources above. Every figure is attributed, and the calculation behind Figure 5 is shown in its caption. If you spot a mistake, write to support@maclenz.com. Apple pages were checked on 6 October 2026. Apple rates and describes its own batteries, and Battery University describes lithium-ion cells in general, so treat the lab figures as a guide to direction. The 80% line and the settings above come from Apple.
See these numbers on your own Mac
MacLenz is a Mac app that is launching soon. Its Performance page shows battery health, charge cycles, temperature, and the watts going into and out of the battery, next to the apps using your Mac.