Make a Galvanoscope
An ammeter is used to measure an electric current. You can make a galvanoscope to detect currents and also to compare two currents.
Small magnetic compass, battery, enamelled copper wire
Take a magnetic compass and wind about 40 turns of enamelled copper wire around it. Use tape to keep the turns in place, keeping the ends of the wire free. The galvanoscope is ready. To test it, connect the free ends of the wire to the two terminals of a cell. You will see that the needle gets deflected. The deflection of the needle tells you that a current is passing through the wire. Test an old cell and a new cell, and note the deflections of the needle in each case. You will see that the deflection is more with the new cell and less with the old cell.