In the box you will get The light, the handlebar mount and four AA batteries. The new Cateye HL-El530 handlebar mount is slick. It is very adjustable to fit large or small diameter handlebars. The tightening knob is on the back so when you mount it if you put the knob on the back of the handlebar you will be fine. I have mounted the light in these pictures on the top of the handlebar. You can mount it on the bottom of the handlebar also. On my own bike I always mount my light under the handlebar for a couple of reasons. One it is more out of the way and two if the bike crashes (I have never crashed but every bike I have ever had has crashed at some time.) The light being under the handlebar is much less likely to get damaged. Also if you put your bike upside down to change a flat the light is out of the way.
The HL-EL530 uses 4 AA batteries and Cateye rates it as 1500 candlepower. I know this is the brightest little light I have ever had. Cateye claims the batteries will last up to 90 hours. This I cannot verify but I have used one for several months and I haven't replaced batteries yet and it is still really bright. I love this light.
The batteries for the Cateye HL-EL530 Install go in really easy. The cute little picture on the flap of the base makes it easy to determine how the batteries go in.
The HL-EL530 light slides onto the handlebar clamp from the Front. After it has been on the bike for a while I always forget if the light comes off the back or the front of the mount. Push the button on the right of the light and slide the light FORWARD to take the light off the bracket.
The body of the EL530 is watertight. The switch which you can see just in front of my thumb is a magnet. The switch is magnetically activated so that there is not a mechanical penetration of the body of the light. This makes it much more likely to stay waterproof long term.
This is a picture of the HL-EL530 mounted upside down. This is how I mount mine. It is less likely to get broken in an accident.
I believe this is the best Handlebar mount light on the market. It will help you ride safely at night. Think outside the Car, Enjoy your bike.