If you live in the south, I found a 12v 8ah lead acid battery for $15 at Academy Sports and Outdoors. They sell it to run automatic deer feeders. Maybe overkill, but I'm planning on adding a 12v horn to my setup and know I won't run out of juice. And the battery fits sideways in my Lowe's tool box trunk perfectly. I drilled a small hole in the side of the box, ran the wires through, and sealed it with clear caulking. I secured the battery in the trunk with industrial strength, self adhesive Velcro. Stays put while riding and allows for removal for charging. I'll try to get some photos uploaded.