I managed to put a 1 cell battery together out of some carbonized comfrey that I carbonized and activated(I don't know for sure if it got activated or not). I used a solution of 25% Real Lemon lemon juice and 75% water and left the carbon in the solution for 24 hours and then rinsed it and baked it in the oven for 4 hours at about 275 degrees Fahrenheit. I made the current collector plates about the size of a credit/debit card from an aluminum soda can that I annealed on top of the cook stove and scrubbed the burned paint off with a Scotch-Brite. I wiped some sanding sealer on the current collectors then pressed the current collectors into the carbonized comfrey powder one at a time and let it dry for a short period of time, it might have been better if I had let them dry overnight. I used paper towel for a separator and comfrey tea for the electrolyte. It took quite a while to charge it the first time but I finally got 1.2 volts out of it. I kept trying to get more voltage but I was never able to and the carbon started flaking off the current collectors before I was able to see how much amperage it would hold/put out. I will have to figure a better way to get the current collector and the carbon together so the carbon won't flake off, I was thinking maybe some aluminum screen, I don't know. I did attempt to carbonize some Cuban Oregano the other day but I don't know if it carbonzied properly or not yet.
I'll keep playing with this and see if I can come up with something worthwhile.
The comfrey tea is made out of the Russian Bocking 14 comfrey leaves, I made it by cutting up the leaves until they filled a 5 gallon bucket and the filled the bucket up with water until it was just over the top of the comfrey, then I let it set and break down for 2 or 3 months. That variety of comfrey can only be grown from root or crown cutting, I got mine from a seller on ebay. I bought it because it is supposed to produce high levels of phosphorous that I was going to use to make my own fertilizer. Besides the phosphorous it is also supposed to pull up whatever minerals you have in your soil from as deep as 10 feet down so I have no Idea what is actually in it. You can get true comfrey seed a lot cheaper but I have heard that the germination rate is not very good.