MONROVIA, Calif. ---- A California-based company, eDrive Systems, has developed a plug-in conversion for the Toyoto Prius that will add about 180 pounds in lithium-ion batteries so that the car can get about 100 mpg and drive up to 35 miles solely on electricity, the Detroit Free Press reported. The eDrive system can be installed in the rear of a Prius in less than a day without touching the motors, engine or hybrid control system up front, according to the company. The lithium-ion battery system fits under the rear cargo carpet. The eDrive system for 2004 and later-year Toyota Priuses will be available in Southern California in early 2006 for an expected retail price (installed) of $10,000-$12,000. The company also plans to announce systems for other hybrid vehicles including the Ford Escape hybrid. The stock nickel-metal hydride battery for the Prius is replaced with an advanced lithium-ion battery system with nearly 20 times the usable energy capacity, eDrive Systems said. The battery control system on the vehicle is also replaced with custom eDrive hardware to encourage the Prius to make use of the expanded battery. At low speeds and mild driving conditions, the Prius will behave like an electric car using only the battery and electric motors. Even at higher speeds when the gasoline engine is running, EDrive injects additional electricity from the battery to further reduce gasoline consumption, the company said.