Laptop light flashing orange...?

The lap top is an Inspiron B130. It's several years old. I have a battery that I already know is very low on juice in my laptop, but I never use it. I use the outlet cord. So why is the 3rd light on the far left corner of my lap top flashing orange still? Is it because the battery inside? Or is there something wrong with my outlet cord? Team of geniuses, please help!