Laptop automatically shutsdown at specific battery.

So, it all started a few months ago, every time my Dell Inspiron got below 20%, it would desplay no proper warning, so what it would do is display a message saying something like "Low battery" 0.5 seconds later, I get a green loading screen and it says Locking..., then I have to restart my laptop.

Now, it still does the exact same with, except it's doing it whenever it gets below 40%.