What happened to my Macbook Air's battery? 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 &quot;Repair battery&quot; 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 &quot;Repair the battery&quot;, as the warning says? If I take it to Apple's official store, will they &quot;repair&quot; it somehow, or will the solution be just a full replacement?
Third-party batteries are a bit of a lottery. There's no telling how closely the specification and quality matches Apple's own parts (which they do not sell on).
The cycle count is a guide to the life of the battery, but that's all. A four-year-old battery is still a four-year-old battery.
You can take it to Apple and get a proper Apple part fitted. It will cost 'some money', but of course part of that is getting a quality product, which will be under guarantee to work properly.
The alternative would be for you to replace it yourself. You can get 'genuine' Apple batteries on eBay and other websites: though as said, Apple don't sell spare parts on the open market, so these are either 'run-ons' from the factory that Apple uses, (or units that didn't meet Quality checks); or they are counterfeit. So again, a bit of a lottery. Or choose a third-party supplier that you feel to be trustworthy, with a reputation for Apple peripherals and parts, rather than someone just trying to cash in on demand.