The Asus battery stats can be misleading. One way to try would be to disable Google sync, but it kind of defeats the purpose if you use Gmail, Google calendar etc.
Does your friend use the dock?
There is a bug in the Asus JB 4.2.1 firmware causing the dock to seriously deplete the battery whenever you re-connect the tablet to the dock while it is on or in deep sleep.
To fix it turn the tablet off, attach it to the dock and restart. Battery performance should be back to normal.
You have to do this each time you disconnect tablet and dock
Sent from my ASUS Transformer Pad TF700T using Tapatalk 4
This is a major problem that is I think for everyone who has done the latest updates. It seems the only way to stop it is to unchecked wifi and mobile network location. Google now won't work but with it on I am getting about 20% of battery compared to normal.
Google need to fix this.