A year and half ago (in Nov. 2019) I bought a second hand Macbook Air (early 2015 model), with a new battery. At first it worked really well... but a few days ago, after only 200 battery cycles, I suddenly noticed a "Repair battery" warning in the status bar. After that, one day the computer shut down when it still had a 49% charge, and then I started noticing that the battery discharged itself much faster than before.
I installed CoconutBattery, and noticed that it said that its current full capacity is only 4600 mAh, while its original design capacity was 7150 mAh. The battery is a Dynapack one and was manufactured in March 2017, but as I said above, it only has 200 cycles.
My questions are:
What happened? The only explanation I can think of is that during the last year (during the lockdown) I've seldom discharged more than 10-20% of the battery in each use. Since I was at home all the time, my usage pattern was pretty much: unplug computer, use it for a couple of hours at most (until the battery was around 80-90%), and then plug it again. (Most times I just used the Macbook plugged in). Could this have affected the battery somehow?
Is there any way to "Repair the battery", as the warning says? If I take it to Apple's official store, will they "repair" it somehow, or will the solution be just a full replacement?