does my battery need replacement so soon?

Hi guys, I bought a galaxy tab 3 t311 twelve months ago. I had used it extensively for internet browsing and editing documents. I can say that I have folowed all guidelines for pampering the battery I.e full and half cycle charges every month, not charging for more than eight hours and I also installed "battery doctor' app and used it everytime I charged my device. However after 8 months of regular usage, the battery started acting funny.it would switch suddenly off at 50% without warning, and sometimes it would still soldier on even at 0% charge! And also the phone would not charge when i plug in the charger cable after restarting it it would eventually get charged. Altough the battery seems fine physically without showing no signs of bloating.i had also reset it 2 times with the battery problem cropping up later.