Sure, we have heard word of lithium ion batteries being possibly implemented in a Prius before, but Mercedes-Benz is going beyond concept speculation with its S400 BlueHybrid, which promises Li-ion HEV action to be hitting the production lines by 2009. At present, that makes the S400 BlueHybrid the first Li-ion HEV with a set mass-production time frame. Current hybrid vehicles use nickel-metal hydride batteries, but the lithium-ion alternatives are known to offer greater efficiency, as well as a better overall weight-to-power ratio. The problem with integrating the Li-ion technology was in securing their stability—they became far too hot to be a viable option in a hybrid vehicle. Fortun ...