The PowerFlare is 192.1 grams as-weighed by me, and I measured it as 4.25" in diameter. Click to see close-ups of the front, rear and internals. It takes a CR123 battery. You can pay $5 each for a CR123 battery, or you can buy them for as little as $1 at batteryjunction.com. Battery life ranges from 8 hours (solid-on high) to 100 hours (single blink). I like the “Rotate” mode, which is good for 15 hours. It also offers an SOS (morse code) rescue mode, good for 24 hours.
Here’s what it looks like in operation (though of course the pattern of the LEDs can’t be seen in a still picture). A carabiner is attached to it in the picture below; that is how I attach it to my bike bag.