2012 Prius v Five: sudden 12v battery failure

The Saga
We've had our Prius v for a few weeks. Bought from a Toyota dealer who serviced the car (oil, filters, rotate) at 114,000 miles) before delivery. The car has been wonderful... until this week. We were on a 900 mile trip to the LA area from Texas, stopped for fuel at about 800 miles, Marino Valley, CA and when I got in to start the car it was completely dead. The day was hot, hitting 115F around Phoenix.

From my manual readings and priuschat readings I thought the 12V battery must have failed. It was 4:15 on a Thursday afternoon.

Lucky/Unlucky
Luckily, there was a Toyota dealer 4 miles away. Unluckily their regular mechanics had left for the day.
Luckily, their recommended tow co. sent a truck within 20 minutes. Unluckily, all three of us could not fit.
Luckily, Enterprise, only 5 minutes away, sent someone to pick me up at the gas station while my wife and son rode with Mr. Towtruck to the dealership. Unluckily, I had to wait to near closing (6PM) to get the car.
Luckily, I got the car and they gave me the "old man pity" discount and I headed for the dealership planning to pick up the familiy and luggage, continue on to Calabasas, drop our son at Pepperdine the next day, and drive back to Marino Valley to retrieve our fixed car on Friday. Lucky (again) moments after I left Enterprise, my son called and told me the service manager swapped in a new 12V and the car was working. Lucky again as I drove around the block and returned the Enterprise car just minutes before they shuttered the shop. Lucky still, Enterprise, in full old-man-pity-mode, voided my rental contract. By the time I walked out of the Enterprise office, our son was pulling in with the Prius. So, in the space of an hour and 45 minutes, we completely broke down, towed the vehicle to the dealer, Enterprise picked me up at the scene of the crime, I rented a car, returned the car, and the Toyota was fixed, all within minutes of closing times at the dealership and Enterprise.

Cost
$95 for the flatbed tow. I hated watching him drag our locked front wheels even the short 20" onto the flatbed. Dwayn, a Jamaican, assured us he understood "Prius" language and all was well.
$200 battery plus $130 install = $330
$10 tip for the Shell gas station attendent who patiently looked up phone numbers for me.
Total $435 for this failure. My wife paid for this, and I think the Toyota dealership reduced it by $50
because the install went quickly.

Happy endings
We continued on to our airbnb rental in Calabasas, washed faces, and went out for one of the best pizzas ever...
the place even had a group of about 10 people who I think were patrons but met to play Irish songs on their violins and gutars.

Discussion
Our car gave us zero warning of any sort of impending failure. The Toyota dealer told my wife and son "120,000 miles and 4 years old, yes, time to replace the 12V". In my opinion, Toyota engineering needs to find a way to detect impending failures, direct dealers to inspect/replace the 12V during routine service appointments (such as this car had 6 weeks prior), or light a dashboard light at certain mileage/age to recommend a new battery. I read another story here where the Prius (non-v) drive had total failure while entering a highway, with no warning signs, and only 1 year after replacement of his 12V.... now THAT would be terrifying.

 

Lesson learned. BUT, who, other than seasoned Priuschat users and Prius dealers would even know to do that? That is why Toyota engineering needs to look for solutions. In all of my own decades of car and battery use, in every case, impending 12V battery failure
came with warning signs; labored cranking, slighly dimming of lighting, hard start on cold mornings.

Leaving owners stranded without warning is not a good formula for owner satisfaction.

 

It was just a "gas" station. The towtruck driver could have given us a jump at $60 vs a tow at $95 but I was not willing to risk a failure on the way to a dealer, 800 miles from home, at closing time. For us we needed some surity. If we were in our home city we might have made the jump decision.

 

Also, from now on, yes, we will install new batteries every 3 years... I just hope we don't forget. If the dealer where we purchased the car even hinted to us to consider replacing the battery we certainly would have done that. Remember this, anything that strands a motorist on the highway is a life or death event. Some things mechanical cannot be predicted or avoided, but in this instance, it would seem that the selling dealer should have given us the choice and Toyota engineering should have provided us with at least a warning. This was a preventable failure event.

 

Thank you for your comments. After reading I put "replace Prius battery" on my calendar for 1 August 2019, three years out. Off to buy the smart charger. We had already assumed the steps you mention regarding no use of accessory mode. We were leaving the headlight switch in AUTO mode, which left the lights on for a minute or so after exiting the car.

 

Also, our 12V completely died, or seemingly so; everything lost complete power, no dome light, no dash lights at all. I left the car unlocked or otherwise would have had to use the metal key to get insidWould a smart charger have helped?

I think this idea also makes sense,

I think we will try the 12V lithium pack. Any wild guess on how far you could drive with one of these? Do they hold their charge over time while stored in the car? Would you connect the pack across the Toyota 12V battery terminals, or disconnect the bad 12V battery and connect the lithium pack to the cables? I just looked at my receipt from Moss Bros and the 12V they installed has a 7-year warranty. Does not state if it is prorated. Frankly, we are still living in some fear that a future failure could result in far worse consequences, but if circumstances are similar to a gas station failure then we could probably avoid the tow and drive to a dealer. Thanks.

 

Related: upon total failure of our 12V, even though our car was unlocked at the pumps, my son could not open the rear hatch even though the doors were unlocked and could be opened. I did not go to the Toyota dealership with the car, but I asked our son if he saw how they opened the rear hatch and he (thinks he) saw them "pull a fuse" under the hood, then open the hatch. This doesn't make logical sense to me. Anyone want to comment?