What are the materials you need to make a battery tester?

You can make two types of battery testers.

The easy one is with a light-bulb.

You need: 2 wires, a light bulb, a fuse, and a battery to test.

If you attach the positive terminal of the bulb to the cathode of the battery, and the negative terminal of the bulb to a fuse and then the fuse to the anode of the battery, you may judge the battery's capacity based on the brightness of the bulb.

(Note: If it does not work, replace the fuse or try without a fuse, the fuse is in case the bulb explodes, which rarely happens. Otherwise, you have a dead battery.)

The hard way is the compass way.

You need: a long wire, a compass, and a battery to test.

Wrap the wire around the compass but leave the two ends open. Connect the two ends to the anode and cathode of your battery. Judge the battery capacity based on the speed of the spinning needle in the compass.

(Note: if it doesn't work, wrap more wire around the battery compass, use a stronger wire, otherwise the battery is dead.)

I, who improved it, am the same person who wrote the answer, I just realized that I wrote battery instead of compassafter I published my answer, so I improved it after I finished.