Replace?

My personal notebook, Asus, suddenly shut down today. Thinking that I had depleted the battery without realising, I plugged in the power charger. My notebook gave a warning message for its battery pack. The message asked for me to consider replacing the battery as it was not charging up at all. 
This notebook has been with me since 2011 and it is still working fine. Wonder if I should just replace the battery pack and use it for another 2-3 years? 
PS. My office notebook has been with me since 2009 and I am still using it! :)