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How To Check Prius 12V Battery


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Hope the Prius boys will find this usefull. I have tried this myself and this method works fine.

The procedure below is for 2004-2009 models. Others must check the battery with a voltmeter or a scan gauge. If anyone has a verified procedure for use on other models please post it.

It's best to eliminate the common, simple and (relatively) cheap causes first. Dying batteries are near the top of this list.

12V car batteries have a lifetime of a few years. Draining a battery will usually permanently degrade it by some amount, and it will never work as well again. If the car starts having strange symptoms, or doesn't start reliably but runs fine, or if KMPL have been dropping and you've eliminated the other simple causes (low tire pressure, lots of recent short trips), test the 12V battery. A failing battery can even reduce KMPL because the car spends more energy trying to keep it charged.


- Without brake pedal, press the Power button once and release to enter ACC mode

- Press and hold the MFD Info button, then turn the headlights on and off three times to enter Maintenance mode; release Info button

- Press “Menu” (on screen)

- Press “Display Check”

- Press “Vehicle Signal Check” - the battery voltage is shown and should be about 12.4 to 12.8 Volts (normal for an unloaded battery)

- Again without brake pedal, press Power button and release to put a current load on the battery - the voltage should stay above 12.0V (if less than 12.0V the battery is not well, or there is a fault or unusual load somewhere)

- Press brake pedal and press Power button once to enter "Ready" mode - the battery is now charging at about 14V (if less than 13.6V or more than 14.4 there may be a problem with the charging circuit)

- Turn car OFF to leave Maintenance mode

Edited by rover
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