If there's one thing a netbook (or a tablet) needs to be really competitive, it's great battery life. No matter how great the software or the hardware, an ultra-mobile machine needs great battery life to be really useful in the field. Unfortunately, the 4-cell battery in the Inspiron Duo isn't quite potent enough to pass muster. It couldn't even last three hours on a full charge in our testing, which is low for a netbook, and very low for a tablet. Many of Asus' netbooks last well over 4 hours, and the iPad can easily last 8, just for comparison. BatteryEater Pro is our go-to testing program, which continually loops a 3D graphic and taxes the CPU until the battery runs dry. It's sort of a worst case scenario but the playing field is level.