It's not recommended to repair Li Ion battery, as that can be dangerous and it can explode.
If a battery has been sitting longer than a certain amount of time w/ or w/o being charged at any point. That battery has reached its life and need to replace it instead. There's plenty of resources to get the battery replaced. But ensure the battery you're looking to replace fits the exact model of your laptop.
I had to replace my laptop battery due to overcharging and had to stay plugged in because it was overworn.
