Confusing Battery behaviour - need advices

IMO there is nothing wrong here.

Battery "health" is an inexact number at best. It is the current full charge capacity divided by the design capacity, and therein lies the problem

Design capacity is the AVERAGE expected capacity value of all batteries of that model. That means some individual batteries have a lower initial value than the average, so "health" may show 98 or 99% on a new computer. My last Macbook Pro showed 102% when new.

Also Health is not linear over time. I like data so here is a spoonful. This is the Coconut battery history from my older Macbook Pro. Health is the third column from the left; cycle count is the second column:

Note that between May 22 2022 and June 25 2022, Health plummeted almost 10 points in a month. But then it recovered. You cannot put faith in a metric that "wiggles."

Also look at those numbers—the battery was NINE years old in Summer 2022! Still works fine.

AFAIK, Health exists to give Apple a threshold value for the eval of batteries under warranty. Their usual policy has been to replace a battery under warranty if it falls under 80% at under 1000 cycles.

Please don't obsess over something so inexact.

On your third-party battery apps:

• Coconut is a reporting app; it alters nothing so I find it acceptable to have on my computers.
• Al Dente Pro appears to CHANGE something, and that potentially conflicts with rather elegant battery/power management software that came with your Mac. I recommend removing that one and asking for a refund.

Here is a bit more detailed information which expands upon @Allan Jones' response:

Keep in mind Apple only just recently showed the Battery Maximum Capacity in macOS so people have never seen how the Lithium Batteries degrade over time. In fact, the Maximum Capacity can fluctuate up & down. For example....a battery with a Full Charge Capacity of 4,315 mAh (battery for MBPro 13" 2017). A 200mAh fluctuation results in a fluctuation of 5%. A 200 mAh fluctuation is not unusual for an Apple Lithium Battery. I only begin to worry about the battery once the fluctuations get to 400 - 500 mAh.

Design Capacity = 4,315 mAh = 100%

Full Charge Capacity = 4,115 mAh = 95%

Before Apple exposed the Battery Maximum Capacity value, the only people who may even have noticed were the users utilizing a third party app such as Coconut Battery to monitor their batteries health.

Unfortunately even most Apple techs are not aware of these specific details. I only discovered it when I analyzed my organization's Apple laptops when people were complaining of battery related issues, but macOS showed the Battery Condition as Normal and the Apple Diagnostics reported no issues either. Apple only cares about when macOS shows the Battery Condition is "Service Recommended", or when the Battery Cycle Count is over 1,000 cycles, or the Apple Diagnostics report a battery failure.

You can take the laptop to an Apple Store to be examined, but they won't do anything unless one of those conditions I mentioned are met.

My recommendation to everyone is to ignore the battery information until the battery no longer performs to your expectations to see if it merits a replacement. Some people may be happy with the battery performance even when the Battery Maximum Capacity is below 80%....it all depends on a user's workload & expectations.

FYI, macOS now includes Optimized Charging so macOS will automatically exercise the battery for you so you don't have to worry about the battery if the laptop is using the power adapter all the time. Part of the Optimized Charging will have the charge level sit at 80% for a while. I believe this is available on USB-C Macs with one of the later update patches to macOS 10.15.x Catalina.

About Optimized Battery Charging - Apple Support