Looking to monitor the 12v battery level

you want to monitor it with the car off, otherwise, you're monitoring the inverter charge level.
i believe you can find bluetooth monitors connected to the battery with phone app.

 

I bought this.

ANCEL BM200 Automotive Battery Monitor for Lithium & Lead-Acid Batteries
https://a.co/d/j2y3J3k

I connected it directly to the battery's terminals and the data is read using Bluetooth. It has memory to for a month of data internally and limited only by your phone capacity once read into your phone. Here's an example of a 5 days span with the focus on a time when the battery heater was on.



This is what the realtime data screen looks like

 

On some earlier gens, there is a series of button presses and switching the headlights on/off that will display the 12v battery voltage on the dash.

Haven't read of any similar process for the 5th gen.

 

Haven't tried it, but procedure from the EU service manuals is:
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1. Ensure that the vehicle is stopped.
2. Turn the ignition switch to ON.
3. Turn off the audio of the radio and display receiver assembly.
4. Turn off the screen from the settings screen.
5. Perform the "Flick from left to right" operation five times on the multi-display shown in the figure. [Figure just shows a long swipe]
   1. Tip: Performing flick operations may cause messages, etc. to appear on the screen, but disregard these and continue performing the flick operations.
6. Flick the multi-display 5 times from right to left as shown in the illustration.
   1. Tip: Make sure to complete the operation within 15 seconds of performing the initial flick from left to right.
7. When diagnosis starts, the service menu screen is displayed.

Tip: If diagnosis does not start due to a failed operation, turn the display on then off and perform the procedure from the start. (Only turning the audio of the radio and display receiver assembly from off to on is not a valid method)
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And it seems that the voltage is under Function Check/Setting > Vehicle Signal

 

Think through what you mean by “level”. There’s voltage, which gives some clue, but by no means a complete picture.

For more in-depth assessment of the battery’s viability, consider a “conductance” tester. Solar BA9 is one example. This is not something you plug into cig lighter socket and done; you need to (periodically) connect it directly to the battery posts.

 

They have limited use in an Hybrid like the Prius though. Their main test is a crank test, which is irrelevant in the Prius. Same for the charge test which tests the voltage ripple from the alternator. Even more so since it requires to rev the engine to a specific RPM, which is something you can't really tell on a Prius, unless you use an app like Hybrid Assistant to get that data.

Unless I'm missing something, it's basically just a glorified voltage tester in a Prius. To me, the voltage monitor I posted is of more use for a Prius. If you have a standard ICE vehicle though, it's nice to have. I have a similar one to test my kid's car battery before the colder months so they aren't left stranded at -30°C.

 

Cold Cranking Amps appears to be the main test these conductance testers do. I would postulate that regardless of a Prius 12 volt battery not being used to turn over the engine, the test is still a good indicator of the battery's viability.

 

The cranking test will fail as it won't register the typical drop of the voltage when cranking the engine. Same thing for the charging test. At least, that's what mine says when I tried in on my Prius Prime.

 

You lost me. The Prius 12 volt batteries are not proprietary “hybrid” batteries. How about an anology:

A man lives in a 2 story house. His aerobic fitness is tested with a stair climb.

now he moves to a one story bungalow. The stair climb test is no longer effective?

 

When the cranking test is performed in an ICE vehicle, the 12V battery is monitored for its voltage dip. That's how it detects if the battery is good or not. The 12V battery in the Prius is not solicitated when the engine spins up so the test is useless. In fact, with my battery tester, the test times out and it never sees that dip.

To use your analogy, in the one story bungalow, the stair test is done with a treadmill without an incline.

 

You're saying the car's starter is used in the test? This is not the case with conductance testers (such as Solar BA9). The car is off for the duration of the test. The test outcome will be the same if the battery's in a hybrid (such as the Prius), a regular car, or removed from the car.

 

How would Toyota test it?

 

I believe they’re using conductance testers (of the Solar BA9 ilk), but high-end ones that can do print-outs.

 

Yes you can even get a battery monitor that is all in one, no phone needed, stick the display somewhere to read voltage, soc. There are also shunt ones that tell the amps going in and out in addition. Like a car from the 50’s had called an ammeter. RV owners often use them to keep track of their 12 volt deep cycle battery.
I have to remember to try the cranking and alternator tests on my truck which now has a battery monitor.
Then there is a regular battery load tester, which can be added to the pile of testers. I think I paid $18 for one.
I’m not installing a shunt battery monitor as the battery has a sensor on the neg terminal. From what I read the Toyota battery sensor is a shunt battery monitor.

 

From above "the battery has a sensor on the neg terminal. From what I read the Toyota battery sensor is a shunt battery monitor."
Do you have any more info on the sensor on the negative terminal ?

 

Ok, mine, when doing a complete test ask to start the car to test the cranking amp and to rev the engine to 2000 RPM to also test the alternator.

 

No, but this video does starting about 5:45.

 

Viewed the entire video once again. It was good a few months ago, and is still good. Just wondering if there is more specific info on the battery shunt and what the car ICU does with the data, how it effects battery charging voltages.

 

When you have a sensor like that at the battery, you can do coulomb counting: integrating the current in and out of the battery, to keep a better idea of its actual state of charge than you can guess from its voltage and temperature. The traction battery has always been managed that way, but the 12 volt battery was not, until gen 4.