Subject: Why won't my Potato Battery work?

I placed a penny and nickel into a potato and measured the voltage and 
milliamps with a Sperry Sp-5A multimeter.  Although I may see an initial 
jump to 0.4 mA it rapidly falls to 0 mA within 10 seconds.  I've tried 
hooking up to 5 potatos in series and see no improvement.  I'm using gator 
clips and 10 guage insulated copper wire to connect the electrodes to the 
meter.  Are the ions in the potato being used up so quickly, or are the 
electrodes becoming fouled somehow?  I'm not sure of my circuit when I hook 
5 potatoes in series.  Should I have one wire or two coming from the first 
four potatoes (the last potato has 2 wires from each electrode to the 
multimeter).  I need this information to help with my science project that 
is due soon.  Thank you for your help. 

Re: Why won't my Potato Battery work?