Phone battery problem

ROSA

I have Samsung galaxy note 3 and the battery drains very quickly ? I search on the web and found that maybe a virus or a spy program installed in my phone , I tried to check the apps installed in my phone using bit defender free antivirus and bit defender show me that there is no malware detected , I tried many antivirus programs and the result "no malware detected " if there is no malware or spy programs on my phone ,  so what is the main problem ???? sometimes the phone shut down by itself !!!!!!! and I noticed when i use the web the battery drains very quickly so please help me I am worried if there is a malicious apps damage my privacy .

 

Rampant

Hi, may it be time to replace the battery or contact the service center?