Since the start of this project I have assembled 5 of these wireless switches. The latest version is rugged and reliable. The range of operation is only about 4 to 6 feet, but that works well for my application. As the battery runs down, the range reduces. 

I use 500 mAh batteries, but the controller will fit 1000 mAh batteries with no problem. I purchase fresh batteries every 4 years or so, but I actually do not know how long a battery will last.

Assembly is somewhat tedious. The detailed instructions are very helpful.