Blackberry Z30 battery draining

Hi All,
I am having problem with my newly Blackberry Z30 battery problem, which i am not sure if its the battery or not. after charging it to its 100% i can only use 20% out of it. immediately, it goes down to 79% it goes off and start rebooting then after a minute or so it will go off completely. if i put it back to charging, it will start charging from 79%. can anyone tell me the problem or is anyone having similar issues? waiting for a quick response.

Thank you.

Hello and welcome to CrackBerry.
Which OS are you using on your phone? Is the phone new or refurbished?

I am currently using 10.2.1.3247 but this was not the initial OS that came with the phone. it is a brand new phone not refurbished. The problem still persist after loading Leaked OS.