2009 Prius Dead Battery

I would try to determine the cause, eg was the rear hatch left open causing the hatch light to stay on? Then I would run the tests which are hopefully the same on your 09:

Prius Battery Check

Do this test after you have driven the car for at least 30 minutes. This will give the battery a chance to be fully charged.

• Put the transmission in Park.
• Engage the parking brake
• Push in the power button. (if not already on)
• Press and hold the "Info" button on the MFD while turning the headlights on and off 4 times.

• Push on Menu in upper right of display screen.
• Push on Display Check
• Push on Vehicle Signal Check
• You will see the 12 volt voltage displayed. In accessory mode the voltage should be 12.6 vdc

• With no electrical accessories on including lights the voltage should be fluctuate between 12.6 and 11.9. The lower the voltage, the less of a charge your battery currently has. If the voltage is very (10v) low do not proceed as the load test might totally discharge your battery. (If you see a voltage around 13.8 you are seeing voltage from the high voltage battery being converted to around 13.8 in an attempt to recharge your battery. This normally does not occur till after you start the engine but might occur earlier if the battery is very drained.)

• You can also test the battery by turning on the headlights, rear window heater and the heater fan. For a new battery the voltage would be around 11.3. If the voltage drops below 10.2 it should definitely be replaced. For voltages in between the lower the voltage, the lower current charge of your battery.

• Push on the brake pedal and push start. You should see Ready in the Speed display. The voltage should now read between 13.8 to 14.2 and higher in winter. This is the charging voltage!

Note: If in doubt disconnect the 12 volt battery completely (start with the negative post to avoid shorting the battery) and hook it up to a battery tester at an auto parts store.

Read more: http://priuschat.com/threads/2005-prius-ran-out-of-gas-now-car-wont-start.110932/#ixzz26sHlub4U​

 

The 12V battery in a Prius can be killed just like in any other car (by leaving interior lights on, etc.), and eventually it will die of old age in any case. Do the tests above and see whether yours is dead. If you're lucky it will be as simple as that, and roughly $200 will set it right.

 

Are you sure you're not confusing the big (traction) battery with the small (12V) battery. I don't think the 12V battery in your 2009 Prius will be under warranty.