This is a variation on the Baghdad Battery using only tap water as an electrolyte. Can you run a light, or recharge a small electronic device using only water? Sure!. While copper and zinc have a very good potential voltage difference , they succumb to mother natures desire for equilibrium very quickly.

Elsewhere on this site you can see examples of various batteries using the redox principle and most lasted only a few days. The metals begin to build up a protective layer on the outside which saves them from further degradation and slows the reaction to a halt. When this happens the battery dies.

 

I discovered something very interesting (to me) while working on an electrolysis machine and using stainless steel rods. One such rod rolled onto my multimeter and produced a small voltage reading. I dropped the rod into a glass of water next to a zinc bolt and confirmed the reading.

I consulted a table of voltage potentials for differing metals and found zinc to be one of the most reactive metals. This is no suprise and is infact used by boats as a sacrificial anode for this reason. Stainless steel contains quite a bit of chromium which lies atthe polar end to zinc on the chart. This means the voltage potential between them when placed in an electrolyte is reasonably large. Stainless steel resists corrosion and so in my eyes would be the perfect material for a battery cathode (if it weren't so damn expensive) as it would hold up to a hostile electrolyte. The zinc anode would be the first to go and so i set about a little testing.

I constructed some test cells using photo cannisters with a zinc and SS bolt pushed through the lid and a gas release pin prick hole. Vinegar was used with water as an electrolyte. Each cell produced around 1.2-1.5 volts however the acidity of the system corroded the zinc after one day. Cola did the same after 2 days. Finally i found a better mix of 20% cola and 80% tap water, and i removed the air hole from the lid. Now the cell produced a steady 1.1-->1.3 volts and after five days still holds 1.1 volts.

The test zinc is from a zinc plated bolt merely tens of microns deep. If it lasts one week then i will find a more pure zinc anode and test again. The following video shows the construction and description of some different water battery cell types. The second video shows a bunch of the cells in series and powering a LED torch.