Battery Life on 15 month old MacBook with M1 CPU

The battery's Full Charge Capacity (FCC, shown as a "Maximum Capacity" percentage) does fluctuate up & down during normal use and is perfectly "normal" for Macs (I don't see this fluctuation with some other OEMs).

There is nothing you can do about it, so don't worry about it. Just use it as a guide and educational experience to understand how the Apple battery works. Remember, Apple never before provided this information to end users although third party apps like Coconut Battery did provide that information.

Use the laptop and once the battery no longer performs to your expectations, then look at the "Maximum Capacity" and Battery Cycle Count and Battery Condition to see if they are showing a problem. If they show a problem, then you can have Apple or an AASP replace the battery. Apple usually won't replace the battery until one or more of the following occurs:

• Maximum Capacity drops below 77% to 80% (this has changed a bit since the value is reported differently in different parts of macOS and the diagnostics)
• Battery Cycle Count is above 1,000 cycles
• Battery Condition shows "Service Recommended"
• Apple Diagnostics report a battery problem

My 2016 MBP's original battery has been at 86% for several months.

Batteries are consumables and no two age alike. Yours may sit at 89% for months ... it may not. Battery degradation is not necessarily linear.

Apple recommends you replace the battery when remaining capacity drops to 80%

Thanks for the example!

Even though @Allan Jones is showing a very old battery, the same thing occurs on brand new batteries, but with smaller fluctuations at first. Plus while the screenshot is showing this over days, the fluctuations can occur every minute with most extreme fluctuations occurring while the system is under heavy load.

Forgot to include some links to Apple articles for options for managing batteries and optimizing battery performance (the first article contains some very important & critical information about battery care since heat & impacts greatly affect battery health):

Batteries - Maximizing Performance - Apple

About Optimized Battery Charging - Apple Support

Here is an real-world example of the fluctuation the HW Tech cites:

That is from the original battery still at work in my 2012 Macbook Pro I bought in Summer 2013. Note that between June 5 2022 and June 25 2022, Health plummeted over 9 percent but recovered. After 10 years of continuous use, the battery is only now beginning to show reduced runtime.

Please don't obsess over an inexact metric.