Sea water battery
With only a few parts you can make a working battery with salt water as it's main ingredient.
This battery can produce 2-5mA at around 1V. Cathode and anode are made out of aluminium foil and graphite taken out from a pencil or old 1.5V battery. Electrolyte, which is actually a paper tissue soaked with salt water, is wound around a graphite rod which represent the anode. The other electrode is cathode and is made out of thin aluminium sheet. It all fits snugly in a film canister with two electrodes wires sticking out. This battery can well be used to power Joule Thief LED circuit.
[ Source: Coggz ]