A fish shocker is a tool that can be used to humanely take a catch. It sends an electric current through the water that temporarily stuns the fish, allowing them to suffocate at the surface instead of being left helpless and possibly struggling for hours. It can also be used to stun crustaceans and other marine life.
A car battery can provide a lot of electrical current, enough to shock most fish. This is why it is commonly used to make a fish shocker. The trick is to get the voltage up high enough. The higher the voltage, the more likely a stunned fish will survive. A high-voltage fish shocker can be made with a permanent magnet DC motor and a voltage doubler circuit.
The motor will run the generator, which will power the circuit to create a very high voltage. A simple voltmeter can be bought for less than 20 dollars and will show exactly how much voltage the battery is generating. A battery with more than 12 volts should be fine for this purpose.
Most stunners are shaped like wands with a pointy end that is electrically connected to two metal prongs. The person holding the wand can then push a button to send an electric current through the electrodes and into the fish. A small amount of current is enough to stun the fish, but it is important to not accidentally shock yourself or anyone else.