i need it to at least power an LCD display on a watch
One of the easiest homemade batteries is the lemon cell. It can be made with a lemon, a copper wire, and a zinc wire. Strip the ends of the wires and stick them into the lemon. If the voltage created by the cell is not high enough you could use multiple lemon cells connected in series.
See sources for making a lemon battery or a potato battery. You'll probably need to hook several of these batteries together in parallel in order to get enough current to power an LCD, but it should be possible. Alternatively, you can use pieces of copper and zinc sheet metal to increase the surface areas of the electrodes in each battery, which will increase the current produced by each battery.
I have noooo idea but you should try a website to find out
