For economic reasons, most of the components created for the One Laptop Per Child project's US$100 notebook computer are innovations on tried-and-true tech, not state-of-the-art. That is, except for one aspect of the device: how the laptop generates and stores power.

Earlier this week, an OLPC official said that the non-profit group plans to test batteries relying on cutting-edge Lithium Ion Phosphate technology in its third batch of beta computers, expected in May.

Also known as LiFePo4, the material is reportedly safer and less toxic than Lithium-Ion (Li-Ion) batteries used in most notebook PCs sold today. While LiFePo4 batteries don't store as much energy as Li-Ion models, they hold more than cheaper Nickel Metal Hydride (NiMH) batteries, which until now the OLPC had said it planned to use.

The announcement, made at the ShmooCon security conference last weekend Washington D.C. was first reported by the independent One Laptop Per Child News blog. It was confirmed by Brian Warshawsky, vice-president of manufacturing for Potenco, a U.S.-based company designing the laptop's other chief innovation: a string-powered generator that looks like a yo-yo.

That generator can, when pulled by an adult for about ten minutes, generate enough electricity to power the laptop for 40 minutes of intensive use, Warshawsky said. The laptops are aimed at children living in Third World poverty conditions, where ubiquitous electrical outlets and clean, steady power won't be present.

Getting cranky

Initially, the OLPC favored an electromagnet-embedded crank that users would turn to generate electricity. The crank, which was first situated on the laptop itself, was moved onto the AC adapter to minimize physical stress to the machine. That design was officially abandoned in September after the design by Squid Labs, Potenco's parent firm, emerged.

Warshawsky, who showed off the latest OLPC unit at the O'Reilly Emerging Technology Conference in San Diego earlier this week, said pulling the string is not only less fatiguing, but it makes the computer more flexible to operate. For instance, a user might attach one end of the recharger to a door or table and pull the other end with his or her leg. And there's no reason a simple wind or water-powered machine couldn't be used to pull the string and charge the computer, he added. (An appealing prospect for any user who's wanted their computer to go fly a kite? -- Eds.)

Potenco also wants to make the recharger durable enough to last ten years or more in rough conditions. For instance, Potenco is evaluating whether or not to add a high-performance polyethylene called Dyneema, which is used in mountain climbing rope, as a core to the string. If the string does break, users can replace it with something as cheap and ubiquitous as nylon fishing line, Warshawsky said.

Charge it

And the recharger, made in China, will be inexpensive: just US$10 to manufacture, Warshawsky said. Potenco sees the recharger as being potentially useful for many other portable devices. "We think it's like the Swiss Army Knife of power," Warshawsky said.

Potenco's recharger work well with NiMH batteries, which are robust enough to handle spiky power sources. "You can throw power at NiMH batteries however you want," Warshawsky said.

The downside? A 5-pack of NiMH batteries can only store 23 watt-hours of energy, about enough juice to power the laptop for only 4.5 hours of active use. Moreover, NiMH batteries are vulnerable to a "memory effect," meaning that even if the batteries can be recharged more than 2,000 times, their maximum charge will decrease over time.

That contrasts with Lithium-Ion batteries, which are not vulnerable to the memory effect and store more energy than NiMH batteries. But recent reports indicate that Li-Ion batteries are at higher risk of exploding. Warshawsky said that in order to use Li-Ion batteries, an additional component such as a capacitor or supercapacitor would need to be added to the laptop to buffer the bursty power source, adding to the weight and cost. LiFePo4 batteries, if they work, will be able to provide the stability of NiMH batteries and a storage capacity closer to that of Li-Ion batteries.