The system automatically uses both batteries - a small one in the tablet section and a bigger one in the base - which drain and charge together when they're connected, and which you don't need to think about unless they stop charging or communicating. (I'm still waiting to hear back from Microsoft on that problem.) In our streaming video tests, which don't tax any part of the system heavily, the battery lasted up to a reasonable 12 hours with brightness initially set to 50. On battery, my test unit wouldn't let me disable autobrightness, which even in a dim environment dropped it unusably low - to about 50 nits. Though Microsoft rates its battery life at 17-plus hours, that's on the optimistic side Microsoft's tests include standby time, which resembles some people's actual work behavior. Microsoft streamlined the detach process so it warns you which apps to close beforehand.

However, despite that flexible-looking hinge, it can't tilt back far as far as I'd like while using it as a clamshell on my lap. I'd never used the Surface Books before in anything other than clamshell mode, and it is kind of useful to be able to choose between essentially a power tablet, where you remove the display, turn it around and dock it facing the other way or as a lightweight tablet that can run very, very lightweight graphics apps. There are things about it I like, or at least want to like. 2x USB-A, 1x USB-C, headphone, 2x Surface Connect

Surface pro 3 brightness not working