Inside the Lenovo Yoga Book is an 8,500 mAh lithium-polymer battery, which equates to around 32 Wh. Lenovo claims the device is good for 13 hours of “general use” and over 70 days of standby; claims that actually seem reasonable now that I’ve used the device.
When I first received the Yoga Book, I assumed that the slim, folding design wouldn’t allow a large battery to fit inside. As it turns out, the combination of a low-power Intel Atom SoC and a battery of reasonable size delivers excellent battery life that should suffice for at least 10 hours of continuous use, if not more. I managed to get 12 hours out of the Yoga Book with a combination of web browsing (using Chrome) and document editing.
The battery tests back up claims of excellent battery life, thanks mostly due to the lower power requirements of Intel's Atom SoC. I guess if you're sacrificing performance you should definitely expect to see better-than-average battery life, which is what the Yoga Book provides.