Battery Health decreasing by 3% in 10 days. One percent in 1 cycle.

mr_green5 wrote:

In just 10 days, my macbook Pro(2021) battery health has dropped from 96% to 93%. Ten days ago, after a year of use, I ran the laptop on battery until it reached 20% charge. The next morning, when I checked again, the charge had unexpectedly dropped to 12%. At that point, the battery cycle was 132 with 95% health. Since then, the battery health has decreased to 93% at 134 cycles today.

When I first purchased my laptop, I used to charge the battery to a full 100%. Later, based on online suggestions, I started limiting the charge to 80–90% max. Despite this, my battery health dropped to 96% at cycle 65 within five months. As I use my laptop continuously for at least 8–9 hours daily, I began keeping the charger plugged in while using it, only running on battery once a week. This resulted in 131 cycles at 96% health, which is 66 cycles in 1 percent health over 15 months.

Recently, I upgraded the OS to the latest patch version because I had skipped the previous one. Since the upgrade and after noticing the drop to 95% health, the battery has decreased further to 93% within just 10 days. It now seems like my battery health is decreasing by 1% with every cycle.

Now, I am worried about battery longevity. Someone please help me on this.

≤ 80% maximum capacity is when Apple suggests the battery is eligible for replacement

The rule of thumb—if you are near the mains leave it plugged in, if you need the portability then run on the battery only—this is how you help optimize your battery charging and extend the working life of your battery by reducing the cycle count.

Get help with your Mac notebook battery

Learn how to optimize the life of the battery in your Mac notebook, fix battery issues, and get service.

If you see Service Recommended on your MacBook Air or MacBook Pro - Apple Support

That computer is a battery-CAPABLE device. It is not optimized as a battery-operated device. (It is NOT an iPhone.)

Your computer performs best when connected to AC power, such as the power adapter. It can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, even with the power adapter connected, the charged state may decline during very stressful work.

When used only on battery, your computer has no extra cushion of power, and may perform more slowly. However, for ordinary non-stressful tasks this may not be objectionable (possibly not even noticeable.)

In general, you should ALWAYS connect a power source when it is possible to do so, and only run on batteries (which could be somewhat slower) when no power sources are at hand. Your Mac will NEVER over-charge.

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The classic way to brute-force improve battery longevity was to create a hysteresis -- to postpone staring a charge cycle until the charged state had declined to a lower level, such as 92 percent, and when topping off, stop before 99 percent. 

Catalina software 10.15.5 and later for MacBook Pro with T2 chip (2018 models and later) includes a new feature called Battery Health Management. Now, based on your usage patterns, this widens the hysteresis to initiate a charge cycle at a lower level, and stop well before 99 percent. 

About battery health management in Mac notebooks - Apple Support

About battery health management in Mac laptops - Apple Support

This relaxes the set points around re-charging (based on your usage patterns) and can improve long term battery lifetimes. When active, recharging MAY stop short of 100 percent charged. Recharging may only begin at a lower level than the previous "normal" threshold of 92 percent or less, typically around 80 percent. If your recent usage patterns demand top battery capacity, the battery will charge completely to be sure you are not stuck out in the wild with no power.

mr_green5 wrote:

But my concern is losing one percent battery health in one cycle and I am afraid to use it on battery.

Need your opinion on this.

The battery's Full Charge Capacity (aka Max Capacity) actually fluctuates up & down all the time. Just ignore it. Once the battery is no longer performing to your expectations, then check its Condition. If at that time the Battery Condition shows "Service Recommended", then replace the battery.

Because the "Service Recommended" condition gets activated at such an early stage for some users, it is best to ignore the condition until the battery is not working to your expectations for battery runtime.

I provided a bit more detail on the fluctuations in this other post here:

macOS battery Maximum Capacity behavior explained -- HWTech - Apple Community

Your computer is a tool for you to use in any way you see fit. YOU should not be a slave to the machine.

Batteries are a wear item, like the soles of your shoes and the tires on your car. Their expected lifetime depends on use (as reflected in Charge cycles) and also in the passage of time, used or not. After a while, you should expect to have to replace the battery.

Battery life also depends on two factors you may be able to control a bit better. Lithium polymer batteries deteriorate when they get too hot, and when they are subject to very deep discharge. These should be avoided when possible.

Despite using these batteries in millions of Apple devices, there is still a lot of of randomness in exactly which battery will fail when.

Apple SUGGESTS (but does not Warrant) that your battery MAY last as long as 1000 charge cycles, provided all other factors are well-controlled.

Apple uses the criterion that a battery that doesn't to hold 80 percent of its original charge capacity should be serviced, and likely replaced.

When designing systems, that 80 percent rule is intended so that, over a Very large sample of devices, almost all will be able to achieve their 'mission' -- still have at least 80 percent capacity at the three-year mark.