Smartphone batteries could soon last up to a week thanks to developments at a company in the United Kingdom. Intelligent Energy has been developing hydrogen fuel cell batteries and has just announced it has signed a development agreement with an unnamed smartphone company.

The battery mixes hydrogen and oxygen together to power the device and only emits heat and water, according to Bloomberg. Thus, any smartphone that uses the technology will need to have small vents to allow the water vapor to escape.

The smartphone company, which Intelligent Energy has described as an 'emerging operator', has put up $7.6 million for the battery's development.

The technology will be similar to that developed for eco-friendly cars but on a smaller scale, The Daily Mail reports.

"We believe embedding fuel cell technology into portable devices provides a solution to the current dilemma of battery life and with consumers demanding more and more from their phones, battery innovation has not kept up," acting manager director Julian Hughes said. "What we offer is a solution that is clean and efficient and means consumers could be truly mobile and free from the constraints of the grid."

The long-life battery could be on the market in about two years, according to Bloomberg.

The company has also said it has been working on a disposable cartridge that would fit into the bottom of smartphones. The cartridges would sell for about $235 (USD).