Over at the Maui Makers hackerspace, member Ryan K showed up with a mess of Lilikoi fruit (also known as passion fruit). Using anodized bolts (source of zinc), some thin copper pipe, wire, switches, LEDs, and a capacitor, he built himself a battery from the fruit.
The Lilikoi vine produces a massive amount of fruit in Hawaii, often creating a nuisance for home-owners who own a plant. The fruit drop and have to be cleaned up, otherwise they rot and attract insects. Ryan tasted one and noticed it was quite acidic and might be a good candidate for a homemade battery.
The fruit charge a 6800 uf capacitor, and when the volt meter hits 3v, the switch can be thrown, letting the green laser emit a short pulse. For those curious, two days later the charge was down to 1.8v. Obviously this is a supply and demand issue they’ll need to sort out.