## Step 6: Test the battery

The final step is to test it out. We need a multimeter to test the battery accurately, but if you want to check it works without a multimeter, just put the two wires on your tongue. If you feel a slight tingle that tastes metallic it works!

If you want to be precise, measure the voltage and current with your multimeter.

My battery produces between 0.8 and 1.1 volts at around 2-5mA. Using a joule thief you could run an LED from this. A larger surface area and stronger electrolyte concentration would improve the battery, but that is up to you to try...

Enjoy!
<p>this is rechargeable</p>
<p></p>
and you also need to use charcoal as it is more porous and will speed up the reaction
first your battery will eventually loose power as the aluminium oxidises.you could speed up the rate by adding hydrogen peroxide or any other oxidiser like kno3.and also connecting a number of them in parallel to get more amps or in serier for voltage
well seeing as an LED uses a small amount of power i would say for a fairly long time
how long will it work?
Can I use a copper rod instead of a carbon rod?
Very nice, Coggz. This is well documented, easy to understand, and cool! I think I'll use this for a science experiment with my daughter.
cool, you can make a mini boat that runs purely on ocean water.
Well, not exactly- the energy comes from the aluminium oxidising to form aluminium oxide. The salt water is just a part of the battery that doesn't contribute energy, because the energy you are releasing is actually the energy that was used by the electrolysis plant to make the aluminium in the first place. Coggz, if you have the relevant electrical theory and the equipment to test it could you find out the internal resistance of this battery? I'm interested to see how much current it could supply, and of course how long it will run for.
But you need the salt water/ionic solution. I know the anode would corrode about 1/2g per hour(i guess), but the boat gets powered by the ocean/saltwater.
I'm not sure quite what you mean ,but when measuring the resistance across the two terminals with a multimeter i get around 53kohm resistance. Is that what you mean?
Not quite- <a rel="nofollow" href="http://en.wikipedia.org/wiki/Internal_resistance">this</a> is what I meant. Any battery cannot supply infinite current so has a theoretical resistance associated with it. <br/><br/>Think of a battery as a perfect voltage source and a resistor connected together (and that can't be separated)- the resistor will limit the current that the battery can provide. A car battery can supply hundreds of amps so has a very small internal resistance, a coin cell has a high internal resistance so cannot provide a high current (which is how they can power LED throwies without burning out the LED).<br/><br/>The internal resistance defines how much power you can draw from a battery- in my example you couldn't power a car starter motor from 12V worth of coin cells, because they can't provide the hundreds of amps required, and I suspect your cell also has a high internal resistance.<br/>
Umm, I don't get it. The foil is already covered in aluminum oxide. So what turns the aluminum oxide back into aluminum to allow this reaction in the first place?
My mistake- the aluminium actually forms aluminium hydroxide, Al(OH)<sub>3</sub>.<br/><a rel="nofollow" href="http://en.wikipedia.org/wiki/Aluminium_battery">More about the chemistry</a><br/><br/>I'm not sure how it deals with the oxide layer, I assume it either takes part in the reaction or is porous enough to allow the electrolyte to react with the pure Al underneath. Either way, the aluminium is supplying the energy.<br/>
BiCarb soda or salt?
Either will work, any mineral salt will work as long as the water is saturated with it (i.e no more can dissolve) I just used bicarbonate of soda as I had it handy
How long can it run an led for?