Toyota’s Prius hybrid has been more successful than GM’s hybrid offerings. Today at the International Geneva Motor Show, GM announced its intention to upgrade the battery packs in its basic hybrid system to deliver more power. Maybe that will help improve sales.

GM’s basic hybrid system uses a souped-up alternator to add brief bursts of power during acceleration. It runs in reverse during braking, converting some of the kinetic energy of the vehicle into electricity. At best, the system improves fuel economy by 20 percent–just a handful of miles per gallon. But it’s less expensive than more sophisticated hybrids like the Prius or GM’s new two-mode hybrids, and it can be incorporated into almost all of GM’s vehicles. As a result, it could be more widespread. GM plans to make about 100,000 of the vehicles a year.

The new battery pack, a lithium-ion pack made by Hitachi, combined with an improved alternator-generator, can deliver three times more power than the company’s older system, which used nickel metal hydride batteries. GM claims that this system will be a perfect complement to another fuel-saving strategy: downsizing the engine and adding a turbocharger for bursts of power. The turbocharger doesn’t kick in right away, and it doesn’t work well at low engine speeds. But the battery and motor kick in right away, compensating for the so-called turbo lag.

The vehicles will go on sale in 2010. At about the same time, GM will offer two other types of vehicles powered by lithium-ion batteries. The most notable is the Volt, an electric vehicle with an onboard gasoline generator for extending driving range.

In the past, lithium-ion batteries were thought to be too dangerous for large battery packs. But new chemistries (in some cases) and elaborately engineered safety systems (in others) are changing this. Lithium-ion batteries are lighter and more compact than the batteries currently used in hybrids.