My 2023 Prius surprisingly wouldn't start today.

The hybrid battery may have had 50% charge, but the car needs the 12v to power up. Everything runs off the 12v, with the exception of the hybrid drivetrain.

 

This indicates that there may be a parasitic drain on the 12V battery or you may have left a dome light (or similar) on to initially drain the 12V, requiring a jump. Have the 12V tested. It may be shot.

 

Are you driving much?

 

For safety, hybrids, and I guess EVs, physically disconnect the traction battery from the drive system when shut down. The 12V is needed to flip that connection back on.

A couple others have reported dead batteries in new Primes. No word on the cause yet.

 

Reminds me of the 12 volt problems in the last generation primes

 

Incompetent dealers are often guilty of "battery abuse".

Leaving an OBD dongle plugged in all the time can do it too since it is
powered all the time.

And to state the two battery situation a little differently:
ALL of the computer boards that actually RUN the car are powered
by the 12 V supply.
No or low 12 V: won't run because the computers won't "boot up".

 

Interesting because how does the app know what the state of charge is without something in the car turned on? I admit I know very little so I ask what may be basic questions. The app says 0 because the 12 volt is low and can’t connect to the app?
Dealers, especially now to get more add on profits, love to install lojack gps theft trackers which also are on. There’s one on my gen 4 and the car drains the12 volt rapidly. Of course my previous gen 4 did as well. I was/am always putting a charger on them if they sit over two days. My 96 Toyota truck, after a week it gets the charger.

 

Something is always on in a modern car. From a cellular connection to the smart key system, even the radio clock. Designed right, the background drain should not be a problem for the factory installed battery. Designed right isn't guaranteed; the energy draw is too much for the supplied battery. Or defective equipment is drawing more than it should. Then there is user error, and that could be things beyond leaving a light on, that they wouldn't consider. I think the manual has a warning about storing SKS fobs too close to the car.

 

Ok, you've got an issue that goes beyond the car. You're basically saying that you've had a total of four Toyotas* where the 12V battery goes/went dead within a week of sitting idle. That is not normal behavior.

I could see the 96 truck if it had an old battery, but the Priuses don't make sense on their own. You mentioned the Lojack. How many of the cars had/have that? Are you financed through the dealership or something and it's one of those systems that disables the car if you miss a payment?

Here's the thing, modern hybrids actually have a pretty steep basic draw compared to vehicles from previous eras. There are a lot of computer systems and relays that must be operated by the 12V system when the main hybrid battery is not fully engaged. But the automakers know this and have developed ways to put the vehicle's electronics into a standby mode that consumes very little power but is still able to sense a wake-up signal.

The two ways this system can fail is if something internal is preventing the system from fully going into standby, or something external keeps waking the car up.

The first problem led to a bunch of early 2019 RAV4s draining their batteries because a software flaw prevented one of the vehicle's computer modules from going into standby. This was fixed by a recall/TSB and a software update. Something plugged into your car like an OBD2 reader or maybe an aftermarket Lojack might do the same thing. Solution? Rip them out(according to the manufacturers' instructions). Other aftermarket components(like stereos) can also cause this if they're installed incorrectly.

**THIS PART'S IMPORTANT**
The second problem is often(though not always) user error. Trollbait obliquely mentioned this, but where do you store your keyfobs when you enter your house/apt? Is your parking spot nearby? It's common for people with attached garages/carports to keep either their regular fob and/or their spare fob just inside their house. I grew up in a house where the spare keys went into a junk drawer just inside the door to the garage. Other families that share vehicles might have a spot to leave the fobs right next to the door. This is a problem.

Hybrids need to do a few things before they're ready to drive. Among those is to use a hydraulic pump to pressurize the brake system since that used to be done with the engine(which might not start right away depending on conditions). But people expect to be able to press the start button on the dash and immediately put the car into gear and go. In order to do that, automakers like Toyota have the car start to wake up before you even get in. They use the key fob to do that. When the car senses the fob approach, it starts the wake-up process(that's why you'll often hear the car make weird noises when you approach). But if the fob is stored too close to the car, the car can go in and out of standby many times as it just sits there. Toyota has built in some precautions to try and prevent this, but nothing is perfect. If you do store a key fob near the car, move it to a different part of your home and see what happens.


*2023 Prius Prime, 2020 Prius Prime, gen4 Prius, 1996 Tacoma/Tundra

 

I am not waiting until the battery is dead, trying to avoid that. I saw under 12 v, and the 2020 Prius Prime had a new 12 v when I bought it. As common charts show, a battery under 12 is getting under 50% discharged, not good for it. Fob stored far away. I know this from 2007 Prius. Which also discharged a lot. The batteries are small for one thing. I bought a couple dc current clamp meters to check the actual amount of parasitic draw. Waiting until some morning and the battery is dead, flying by seat of pants, is what I’m avoiding.

 

The main battery is disconnected when off for safety purposes.
When’ready’, the inverter charges the 12v regardless of engine or motors being used.

 

I suspect the 12v is damaged. Take it to Toyota for testing and warranty

 

I'll ask the obvious; have you made any electronic modifications or additions since your purchase? Such as a dash cam that is always powered on, etc..

 

Unless you took a drive of over an hour, or hooked the 12V up to a charger, there is a good chance it was never fully recharged since it died.

Just sitting in the car ccan cause systems, like the push button start, to stay in wake mode, draining more power from the the 12V.

 

If you want to really know what’s going on, get a dc current clamp meter to measure charging or discharging current, and a volt meter. It should be pretty easy with battery in the trunk. They are inexpensive. I’m still fiddling with measuring my 2020, but maybe there are already threads with results on older models.

 

Brought the car in for service. drove over 200 km after, today I got in the car to change some settings (tried to turn on the key proximity lock but that's a different story) and the 12v ended up draining in a couple minutes and the car wouldn't start.
The back hatch was able to be opened and I boosted it with my battery booster, I've got it charging with my 12v charger and I plan on getting the battery tested sooner than later.

 

• Do regular long trips.
• Do not sit in the car with anything on unless the car is in the READY mode.
• Do not leave the AC charger plugged in for longer than overnight, as it drains the 12-V battery.

 

I'm surprised that toyota didn't think to put a 12v battery maintainer in the vehicle also powered by the AC charger or at least have anything that would draw from the 12v battery powered from the AC input as well.