I spent some time searching for an answer as to how to check battery voltage. There were some posts that were close, but not close enough for my model, purchased in Kingston, Ontario, Canada. I finally have the answer for my model. This procedure is for a 2012 Prius with a display screen as follows. Left side panel, --------Right side panel top to bottom ----------top to bottom PWR VOL knob -------TUNE SCROLL knob Up arrow --------------Right arrow SEEK ------------------SETUP TRACK---------------- CAR AUDIO ----------------Phone symbol blank section ----------blank section Checking 12v Battery Health You can easily check out your battery status/charging system by using the MFD Service Menu. 1 Get your Prius into "Accessory Mode" . Press the power button without touching the brake pedal. 2 Put the MFD into "Service Menu" mode (green) Press and hold the "CAR" button on the MFD while turning the headlights on and off 4 times. 3 Press the "Function Check / Setting" field on the screen. 4 The "Function Check / Setting menu will appear. 5 Press the "Vehicle Signal" field. 6 The "Vehicle Signal Check Mode" screen will appear, showing Battery 11.9v ---------SPEED 0 Km/h IG OFF ---------------TAIL OFF PKB ON --------------ADIM/TCAN BRIGHT REV OFF The 12v battery voltage will be one of the items listed. 7 Put a small load on the battery by pressing the power button again without touching the brake pedal. If the voltage drops significantly, you need a new battery. 8 Now get your Prius into "Ready Mode" - step on the brake and press the power button. The battery voltage should immediately rise to about 13.8 volts. 9 Shutting the car down will reset the system back to normal operation. To put the MFD into "Diagnosis Check" mode 1 Get your Prius into "Accessory Mode" . Press the power button without touching the brake pedal. 2 Put the MFD into "Diagnosis Check" mode (red) Press and hold the "SETUP" button on the MFD while turning the headlights on and off 4 times. 3 A red "Diagnosis Check USA" screen will appear.
