I wouldn't bother with any anti virus and don't read too much into battery stats for wifi usage and idle usage. The most important battery stat is screen time usage. Our Hudl ranges between 6-8 hours screen time depending on what we are doing with it on a full charge to zero.
When after a full charge and I am on it for a couple of hours, and when it goes down to about 50%, it sometimes difficult to power off, or the page freezes for a while, till I start to recharge it again. Don't know if anyone else had this happen to them?
. I did the 3 hour charge when I first got it.