Laptop shuts down and says replace battery??

Hello,

I'm just wondering what it means when my laptop shuts down, but it turns on but it says my battery ocupacity is low and that I need to replace the battery?
I haven't done any damage to the laptop except dropping it ONCE - wasn't a long fall -.
My laptop is ALWAYS charging.
Never off the charger.
But it shut down when I was listening to music through AUX and I turned it back on thinking it died and a black screen popped up with words saying my battery ocupacity is low and that I need to replace the battery.
Please help!!!
My laptop is only 1 year old!!!!!! ************