I picked up a bunch of lasers - photo on my web site in the misc for sale section - these are more powerful than laser pointers - run nicely with two AAA cells or AA - the cell in the photo is AAA, diameter is 0.410 inches, length is 1.25 inches
these have pigtail wires so you can put the batteries in the handle of your hollowing rig - that will reduce unsprung weight and improve reliability. you can modify an old flashlight if you like to be the battery holder.