That would be a good question. They're identically spec'd machines of roughly the same age with batteries that are within 1% full charge capacity. They re both

That would be a good question. They're identically spec'd machines of roughly the same age with batteries that are within 1% full charge capacity. They re both on the same wifi, Bluetooth is off. Display brightness varies, but neither is cranked, I'm not sure what else hardware wise could be seriously different. The biggest difference is the os. I will concede that usage varies, hers hits Facebook, mine Twitter. And I run virtualbox but she doesn't. We're both running safari, chrome and mail.