Not sure what happened when I got home last night

you may be overthinking it. if you locked the doors, it couldn't have been on.

isn't it possible the battery was simply on its last legs?

pull the top off and check the date code

 

Have you done anything to address this known issue? ( 12v battery | PriusChat )

Have you checked the 12v battery voltage already ?

12 batteries don't last forever. Do you know for a fact that it was recently replaced ?

 

i drive mine everyday. one morning i started it, no problem, drove four miles, no problem, parked for an hour, came back and the door wouldn't unlock.
unlocked with the key, pushed the go button, nothing.

aaa arrived an hour later, battery was 4.4 volts

replaced the 7 year old battery, no problems since

 

Which part of NorCal are you in, is there a Pep Boys nearby?

 

You can check the voltage from your MFD. it’s actually better to do that rather than starting and driving the car then checking it

 

Yes it legit. I’ve used it many times. I do the secret button trick though, not the headlight switch method.

https://www.google.com/amp/s/idoneitmyself.com/2015/01/25/entering-the-maintenance-or-inspection-mode-on-a-prius-1st-gen-and-2nd-gen/amp/

 

I would check the battery voltage with a multi-meter, at the under-hood jump point, first thing in the morning, after sitting overnight. Preferably with the hood popped the night before, so that there's no "waking up" off the car.

Better by far, get something like Solar BA9 (or one of a slew of other similar) automotive battery electronic load tester.

 

Once you are positive the battery is the/a problem.

Order online for 25% off (linked below) or Call and see which Pep Boys location has a Bosch AGM in stock (they all should) :

• Part#: 51-440BAGM
• SKU: 647478

Bosch Premium Performance Battery Group, Size 51 | 647478 | Pep Boys

They're advertising 25% off online orders, and then you can pick it up at a store. You don't have to actually pay for it online (no CC needed), you can pay upon pick it up. If you can't order this at work, home, phone, then one of the employees can help you order it from their computer for an in-store pickup. You'll need a reservation for installation, if required.

There is a $40 rebate on Bosch/Champion AGM batteries. http://img.rewardpromo.com/1/7554/21853.pdf

Hard to beat Pep Boys this time of the year, even with the $15 install fee (not required if you DIY).

 

If your battery was dead to the point you needed a jump, then it would take a Prius 8-12 hours in READY mode to charge the battery enough to continue with only the damage caused by 1 low voltage cycle.

If you got a jump, drove to work, and parked it (off, not READY), all within 4-hours, there's no way that battery even had a chance to charge up.

 

I tried that once. As soon as I lifted the hood the car alarm went off.

 

Also make sure someone hasn’t changed over your battery terminals to the US size. That happened to me and I had to buy new JIS sized ones

 

Sounds like the battery’s done. Car dealers are notoriously cheap. They might have replaced the battery with a used one, could have lied too.

 

Any 12v battery that doesn't start a Prius is automatically on it's last leg. That's the thing with the Prius. In a "normal" car you have a starter that draws yuuuuuge amounts of power from the 12v battery to "crank" the engine and start the car. When your battery gets just a little itty bitty bit weak, it starts making more noise a good audible indication of it being low. It may even still start with more coaxing and retrying. Eventually you get to where you hear it spinning the engine and barking like a crazed manatee and the car won't start. Jump the car, the battery is float charged back up to the 12.4 to 12.8 volts the battery normally sits at by the 13.8v to 14.4v alternator in the car that is feeding it 40A or 80A or 200A depending on the vehicle. The low battery will get super hot and vent but take the charge.

Now the Prius doesn't do any of that. You get in the car, the Prius primes the brakes which can be a 30A draw for a couple seconds. But then no draw but the dome lights. You press the brake pedal and on button, and it flips 3 relays in sequence to attach the HV battery to the inverter. 1 to precharge the high voltage positive and the HV ground. Then it flips the full power high voltage positive. Then it turns off the precharge relay. Click-click-click. That can be done with less than 9v. A 12v battery is considered low at 12.4v. It is considered DEAD at 11v. At 9v, you have a severely discharge battery potentially with 2 or more completely failed cells inside. Yet somehow it can still manage to start the car. And when the battery is 12.8v it sounds EXACTLY like when the battery is 9v. Because it just does click-click-click and that's it. The HV battery then supplies the power to MG1 to spin/crank the engine. And the second the inverter is on, the 12v is being charged by a CVCC controller in the inverter that supplies 13.8v-14.4v at up to 12A (15A relay). If the battery is dead, it will supply 12A at a super low voltage to trickle charge the battery up. Charging a DEAD DEAD DEAD battery at 12A back to where it is healthy will take 8-12 hours.