Gravity battery demo turns falls into phone-charging power

A new demonstration model shows how a gravity battery can turn repeated drops into electricity, producing 13 watts at peak and 58% efficiency. The builder says the setup isn’t practical for everyday charging—reportedly requiring 394 drops to fully charge an iP

On a workbench. the idea is simple: lift something heavy. hold the energy in potential form. then let it fall and harvest the motion as electricity. Gravity batteries have floated around as a concept for years—but one recent build takes that premise and turns it into a working demonstration you can point to. measure. and repeat.

The demonstration comes from Valeriamayara22, who describes how to construct a gravity-battery model that can generate electricity as the weight drops. The setup is designed around a known tradeoff: it’s not free energy. The energy has to come from somewhere to raise the mass in the first place.

In this model, the height is 1.8 meters and the mass is 15.65 kg. With those parameters, the system reaches 13 W peak output and 58% efficiency, as described in the post. The efficiency figure is framed as a comparison between potential energy stored and the energy produced. The builder also emphasizes that the system’s energy isn’t “mysteriously better” after it warms up—one of the striking claims is that it stores as much energy on its 1. 000. 000th charge as it does on the first. assuming the chain stays lubricated.

Still, the project is more proof-of-mechanics than a new charger for your pocket. The post reportedly puts the charging burden at 394 drops of the weight to fully charge an iPhone 16. That doesn’t make it practical in daily life. but it does show what’s involved when you try to translate potential energy into usable power.

The mechanical heart of the build leans on bike parts: a bicycle chain and sprockets. That choice matters because mechanical systems have their own timing problem—like wind power. when energy comes from motion. you either use it immediately or you lose it. The battery acts as a buffer, storing what the drop can provide so the electricity can be drawn when needed.

A build like this is also a real-world engineering exercise, not just a thought experiment. The cost of the build is about $400. and the project comes with a GitHub repository containing the files for anyone who wants to try it. The builder also notes that if you change how the weight is lifted—using some other energy source rather than whatever the demo assumes—then the overall energy calculation shifts too. In other words. the “efficiency” number discussed is about potential energy versus output energy from the gravity mechanism. not a full accounting of the energy used upstream.

Scaling is possible in theory, the post suggests: a practical gravity system can be very large. The question for anyone watching this demo isn’t whether gravity can be converted into electricity—this model already answers that—but what it would take to make that conversion competitive. efficient. and convenient outside a lab-like setup.

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