For power I'm using a 3v CR123A rechargeable battery. It fits into a custom fit holder that uses copper tape and braided wire to connect to the circuit. An on/off switch lets you shut it off while not in use to save the battery. The batteries are apparently a commonly used size for flashlights, I got a pack of them on Amazon with a charger. They are 600maH and in my own unsophisticated testing they will last for about 12 hours while sending an HTTP request once per minute. Given the extra time you get for turning it off, and the batteries being rechargeable this puts them in an acceptable range for my purposes.