A Kickstarter campaign has started for a spare battery pack claimed to charge from your movement.

The device, dubbed Ampy, is currently a prototype, and its creators said you can strap it on and charge it while you walk, run, or ride a bike, according to TechCrunch.

"As you move, your motion couples with the magnets inside Ampy's inductors, producing electricity and recharging the internal lithium ion battery," Ampy co-founder Tejas Shastry explained, adding that the user produces more energy the more and faster they move.

"We've found that running is one of the best ways to generate energy Ampy outputting up to hundreds of milliwatts," Shastry said.

The battery can hold 1000mAh of charge, which won't be enough to completely charge most smartphones.

Users will be able to generate close to three hours of battery life by walking about 10,000 steps or running for 30 minutes, TechNewsWorld reported. The battery can also be charged by plugging it into an electrical outlet.

The campaign is making Ampy available in several different forms. The standalone unit is available for $85, but backers can also get the unit with an accessory pack (featuring an Ampy protective sleeve, armband and clip) for $105. The Ampy 2-Pack, which comes with two accessory kits, is priced at $195, and the Family and Friends pack, which includes a set of five batteries, costs $425.

The Ampy team has already surpassed its original goal of $100,000, having raised over $245,000 so far, TechCrunch reported. Potential backers have 10 days left to show their support, and shipping will begin in June 2015.