Car Battery Failure
Open the hood of the Prius and locate the battery that's used to power the car itself. Place another vehicle with a working battery in front of the Prius, with the front bumpers almost touching.
Turn the working car off and open that car's hood. Find the battery and clip the standard jumper cables to the appropriate battery terminals (red for positive and black for negative).
Clip the other end of the cables to the terminals on the battery of the Prius.
Turn on the working vehicle and let it rev for a few seconds. Once the working vehicle is on, start the Prius. The Prius car battery should come to life and the car should start.
Computer Battery Failure
Open the rear of the Prius and locate the computer battery access points, which are connected to the auxiliary battery in the rear cargo area.
Plug one end of the 12-volt power cable into the 12-volt power supply. Plug the other ends into the battery connectors located in the Prius.
Start the power supply and wait until it's fully powered up (this usually takes a few seconds).
Start the Prius once the power supply is fully powered up. The on-board computer should begin to operate.