So, the extended battery will give me at least 8 hours working time, enough to use it all day at work (next to my work notebook) without worrying about the battery.

Specs: Everun Large Battery, 4000 mAh LI-ION, 11-12 hours
Shop: www.mobilx.eu
As you can see on the picture, the Everun gets about 0,5 mm thicker. There's also a video on YouTube showing the increased thickness. That's the trade off for more power.