14-year-old Instructables user Angelo S. Casimiro put up a step-by-step fabrication process that can be completed in as little as 10 minutes and can power a small calculator or a similar low-consumption device.
If you’re just before an exam, but forgot to buy a battery for your calculator, you can always revert to …water! Yes, you’ve read correctly: water can successfully replace the small battery of a calculator which can perform the same complicated math calculations that you couldn’t.
All you need is a carbon or a copper rod that you can take from a used AA battery, a 1x 1 inch aluminum foil, a small cylindrical container, a 2-3 inch wire, multi purpose pliers and a glue gun.
First of all, perforate the cylindrical container on the bottom and its lower side. Then stick the carbon rod with some glue as the positive rod and the foil as the negative plate. Next, after you have taken off the back of the calculator with a screwdriver, you can go on to attaching the water battery to the calculator, without forgetting to disconnect the solar panel.
Speaking of water, our advice would be to actually use water with salt or even vinegar instead if plain water, if you want to get very good results. After re-attaching the back side, your work is completed. You’re now off to making complicated calculations again, just don’t forget to refill from time to time!