The Samsung Ativ Tab comes with an 8200mAh battery, which on paper is a reasonable size - coming in at just below the 9000mAh Google Nexus 10 and a fair bit higher than the 6000mAh Sony Xperia Tablet S, but well below the 11,560mAh iPad 4.
In actual performance terms we were very impressed with it. After around nine hours of fairly heavy mixed usage - doing everything from playing games, to watching videos, web browsing and listening to music - the battery was still at 35%, and that was with the screen at full brightness much of the time.
In our standard test - setting emails and social networks to send push notifications, turning on Wi-Fi, putting the screen to full brightness and then running a 90 minute video from a fully charged battery, the Samsung Ativ Tab still had an impressive 88% battery left at the end.
There are a few battery saving options available, such as changing the screen brightness (or setting it to auto) and changing the amount of time before the screen dims or turns off, but in general you probably won't even need them.
Samsung's Ativ Tab definitely has one of the more impressive battery lives we've seen on a tablet, and it should be more than enough for most users.