Take a plastic bucket, fill with water, put two pieces of scrap metal (aluminium will do good) in it, wire them to the poles of the battery while taking care they do not touch each other. Iron is ok, but the residue is a dirty mess. Don't use copper as the outcome is toxic.

Then start pouring in some salt slowly until you have a sufficient reaction (gas production, but no excessive heat up).

This is a cheap and high performance load with integrated cooling device.

This will stop working once a certain voltage depending on the scrap metal pieces used is reached. After checking the voltage you can carefully connect the metal pieces under water. Wear goggles when doing this.

Last hint: do this outdoors only or you will blow up your house with the generated hydrogen.

beware. This solution is partially hazardous. Don't do this inside a building, near sources of ignition or delicate and expensive equipment. Do not breathe any developing gasses. If unsure, resort to the other suggested solutions.

Take a plastic bucket, fill with water, put two pieces of scrap metal (aluminium will do good) in it, wire them to the poles of the battery while taking care they do not touch each other. Iron is ok, but the residue is a dirty mess. Don't use copper as the outcome is toxic.

Then start pouring in some salt slowly until you have a sufficient reaction (gas production, but no excessive heat up). Don't breathe this!

This is a cheap and high performance load with integrated cooling device.

This will stop working once a certain voltage depending on the scrap metal pieces used is reached. After checking the voltage you can carefully connect the metal pieces under water. Wear goggles when doing this.

Last hint: do this outdoors only or you will blow up your house with the generated hydrogen.