Gravity batteries aren’t exactly a new idea. You can store energy by lifting something heavy, converting kinetic energy into potential energy. To get it back, you let the mass fall and convert that motion to electricity. [Valeriamayara22] shows how to build a working demonstration model of such a system.

This isn’t free energy. Something has to lift the weight. In this case, the height is 1.8 meters, and the mass is 15.65 kg. Even so, the model achieves 13 W peak output and 58% efficiency, according to the post. Reportedly, it takes 394 drops of the weight to fully charge an iPhone 16, so this isn’t a practical project, but it does show how a gravity battery works. One nice thing is that the system stores as much energy on its 1,000,000 th charge as it does on the first one, especially if you keep the chain lubricated. Try that with a chemical battery.

The mechanical part uses a bicycle chain and some sprockets. There is a battery to even things out since, like wind power, when you make energy with a mechanical battery, you either use it now or lose it.

The cost of the build is about $400, and there’s a GitHub repo with all the files if you want to take your own shot at it. The energy efficiency number references the potential energy stored versus the energy produced. Obviously, if you are using some other energy source to lift the weight, that’s another calculation.

As you might expect, a practical system like this can be very large.