Im running the 4 GB Ram with 128 Hard Drive. So I bought the 13" version on eBay and the guy shipped it last Thursday....ON SLEEP MODE. I didn't receive it until today and the battery was at 96%. Ive been using it all day today with WiFi since 2 pm and its only at 7 pm. Sorry but i haven't used a mac since the Macbook Pro from 2005. So the battery improvement is huge to me. Especially for something this thin...Its running Yosemite too..