What are the allowable voltage levels for the 12v aux bat?

The 12 volt battery needs to be replaced.

The 14 volts is the Inverter DC to DC 12 volt battery charge voltage pretty much the same as most other cars. That's the voltage of the car charging the battery. Your interested in what the battery voltage looks like with no car charge participation and under load.

Get a digital volt meter and measure across the front jump points. With the CAR OFF turn on the headlights and measure the dc voltage across the jump points. My guess is it will be 11 volts battery toast. If so replace it asap.

 

Start by getting a digital multimeter and measuring the voltage with the car off, after it's sat overnight.

Then for a better assessment of the battery's health, either get a battery retailer (or a dealership) to do a digital load test, get a verdict, or look into DIY level digital load tester, something like Solar BA5.

 

what trouble light did you get? i didn't know there was a warning for a bad 12v.

 

I agree with what others have posted: for any weird electrical problems with the Prius, the first thing is to check the 12V battery. If the 12V is in fact okay, than see this thread: 2006 Prius with error codes C1241 and C1378 | PriusChat

~13.5 to 14.5 is normal while in Ready mode. After the car is off after sitting overnight, you should see ~12.2-12.8 with a digital multimeter with the car off. Less than this points to a bad 12V if the battery should be fully charged. The voltage constantly reading in the 14s while driving often indicates a bad battery as the inverter will push up the voltage to try to charge the battery. The proper test of the battery is a load test - a lot of local auto parts stores can perform this for free (at least in the US).

 

READ my post #5 & #8.
Run the test outlined in #5. Read #8 to understand whhat the declining voltages mean.
Is my inverter coolant pump slowly failing? | PriusChat

You are not providing enough information, so the following is just speculation.
1) You don't drive enough on a daily/weekly basis. This will put the battery in a undercharged state.
2) The battery may have had a sever discharge experience, which will reduce its life expectancy.
3) You sit in the car listening to the radio, in ACC mode, for prolonged periods of time. This will definetly help discharge the battery and take its toll, esp if #1 above is true.
4) The 12V battery is still original to the car when it left Japan. Anywhere from 8 (2009 model year)-13 (2004 model year) years old.

 

some stored codes are not relevant.

 

yep 10 volts is a dead battery. if it was a normal car with a standard starter motor it would go click when you tried to start it.

oh you never said it sat for 12 months. We could have all told you it was done.

 

Time to get a new battery. At 10V in good temps, it might still be enough to power the ECUs to get the car going, but expect to be stranded one day soon.

Good idea to get one of the smart AGM compatible chargers I listed in post #8, on a different thread.

 

But there are no lights on the dash with this one. There aren't any DTCs per se for a bad battery, but ECUs get upset with low 12 V voltage and will set codes, such as this one set by the ABS/ASC/TRAC ECU. Click on the freeze frame data and it will show you the B+ voltage at the time the code was set. You will find it is less than 10.5 V.

No, it doesn't and it doesn't push the voltage up. 14.0-14.4 V is the normal charging voltage. All it tells you is the battery is flat and it is being charged in earnest.

As the others have said, your 12 V battery is a goner. Nothing to do but replace it.