12" MacBook battery is dead after 386 cycles I have an early 2015 12" MacBook 512 GB SSD with 8 GB RAM.

I have used my it nearly daily since I bought it brand new. I have never exposed it to high temperature, always working in AC room with a temperature around 24 degrees Celsius. Never worked in bed, but always on the table. I always care of my computer in the best possible way.

The Battery has major issues, the battery is sometimes charging till 100%, sometimes it drops to 20% and charging only till this number. Sometimes I can run my MacBook without charger plugged and sometimes it won't even start if it's not plugged.

The battery side is probably a little bit inflated so the case doesn't fit together as on another side. Looks like the battery somehow got bigger.

Any ideas why is this happening? And if Apple will care it like some hardware issues from their side so they will change it? The battery is only 386 of 1000 cycles they told me so it is absolutely outrageous on the machine for $2000 at that time.
An inflated/bulging battery is a safety risk and you should get it repaired ASAP. The reason for this could be anything from manufacturing defects to improper care.

If you got AppleCare when you bought your Mac, you may still be able to replace the battery for free. Otherwise, Apple won't change the battery for free, as warranties only last one year.(see here)

If you schedule a repair without AppleCare or warranty, it can cost anywhere from $129-199, depending on your Mac's model. You can schedule a repair here.

Or, if you are willing to take the risk, you can replace the battery on your own using an iFixit guide.