It is the size of 2 minidiscs with their cases stacked together, and weighs approximately 3 minidiscs. It should fit quite nicely in your shirt pocket as it is THAT small and THAT light. On top of that, the unit is very sturdy. It is made of a strong magnesium alloy. Only the rechargeable battery door seems weak, it is made of plastic.
Battery life is excellent.
The supplied rechargeable battery lasts 12 hours for playback, and 6 hours for recording. It took less than 3 hours to charge a fully drained battery. But the big attention grabber is its size and weight. It takes 5 seconds to start playing a minidisc from a stop, and about 2.5 seconds to switch tracks while playing. I think this problem came part from Sony's solution to decrease power consumption on the unit which result in better battery life.