at the optimum temperature and optimum charge level. Like the second generation Prius, the third generation Prius battery pack is made up of the same type of 1.2 volt cells. It has 28 modules of 6 cells for a total nominal voltage of only 201.6 volts. A boost converter is used to produce 500 volt DC supply voltage for the inverters for MG1 and MG2. The car's electronics only allow 40% of total rated capacity of the battery pack (6.5 ampere-hour) to be used in order to prolong the battery life. As a result, the SoC is allowed to vary only between 40% and 80% of the rated full charge. The battery used in the Highlander Hybrid and the Lexus RX 400h was packaged in a different metal battery casing with 240 cells that deliver high voltage of 288 volts. A button labelled "EV" maintains electric vehicle mode after being powered on and under most low-load conditions at less than if the traction battery has enough charge. This permits all-electric driving with no fuel consumption for up to . However, the HSD software switches to EV mode automatically whenever it can. Only the Toyota Prius Plug-in Hybrid has a longer driving all-electric range in blended operation electric-gasoline of (EPA rating) until the battery is depleted. The Prius PHEV is outfitted with 4.4 kWh lithium-ion batteries co-developed with Panasonic that weighs compared with the nickel-metal hydride battery of the third generation Prius, which has a capacity of only 1.3 kWh, and weighs . The larger battery pack enables all-electric operation at higher speeds and longer distances than the conventional Prius hybrid. The following table details the HV battery capacity for several Lexus and Toyota vehicles. Operation The HSD drive works by shunting electrical power between the two motor generators, running off the battery pack, to even out the load on the internal combustion engine. Since a power boost from the electrical motors is available for periods of rapid acceleration, the ICE can be downsized to match only the average load on the car, rather than sized by peak power demands for rapid acceleration. The smaller internal combustion engine can be designed to run more efficiently. Furthermore, during normal operation the engine can be operated at or near its ideal speed and torque level for power, economy, or emissions, with the battery pack absorbing or supplying power as appropriate to balance the