Why doesn't the app indicate 12V battery level?

If even one time. I've been left once or twice staring at a jump pack that read 100% a moment ago now reading 0% in less time than it took me to step from the engine bay to the door and reach in and try to start the car.

In my gen 3, I've now taken to disconnecting the battery cable (easy in gen 3, it's right there in the underhood fusebox) if I think the battery might be that drained, then making the car READY with the booster pack, then plugging the battery back in.

That's harder in gen 1 or 2, with no easy up-front way to disconnect the battery, have to get in the hatch. I don't know the story with the newer generations.

 

No doubt you've done all this but for others reading this thread and having doubts about their vehicles cellular connectivity (and has the initially free or subscription Drive Connect service) ...

Try using the "Hey Toyota" voice assistant liberally and ask how is the weather in "Moose Jaw". That'd certainly kick the vehicles cellular electronics into action whenever you have the feeling you're in a less than ideal location. The absence or speed of the reply might be quite telling.

And, maybe if you ever want to ratchet up Toyota's interest/involvement from their side with 12-v battery issues use the SOS button to summon their roadside assistance for a jump start. Of course, when you have your own booster you can cancel that request. But, if you do have time, let them incur some expense. At a minimum, it serves as another data point for you to assess whether the SOS conversation over the vehicles cellular connection at that moment sounds good and clear and connected. And, Toyota will no doubt have a record of when and where you called from. (and it seems from reply #8 that the cellular connection can possibly work even when there isn't enough power to start the vehicle ... that would be appropriate for an SOS service)

Finally, I found a couple pages from the Service Manual indicating that their Techstream system does log things related to the Data Connect Module (DCM). You'll see in the "System Operation Status Example" that it'll log occurrence time, whether roaming was on or off, if the vehicle was in a service area or not and what the strength of the cellular signal received by the vehicle was. No doubt, they can pull a report to coincide with the blocks of time you know you've had problems within recent history.



And, if desired, the best do-it-yourself log of when a 12-v battery might be experiencing drain or charging can be had with a bluetooth 12-v battery monitor that in my case records the voltage every 2 minutes 24x7. I've learned what happens when the DCM is involved or that darn EVAP pump kicks in for 10 minutes in the middle of the night when I haven't been near the car for hours. It all leads to discovery and learning and understanding.

 

Huh? OK, I understand.

I only mentioned those Toyota apps and services because they absolutely will use the vehicles cellular connection and lend some real test to your belief about cellular connectivity being why your 12-v battery drains. It was not about advocating to use those terrible Toyota apps in any other way (I sure don't). But, unless your phone and Google Apps are using the vehicles cellular connection (which it wouldn't) then you wouldn't have a helpful way to gain insight into your beliefs. It's entirely possible your phone and vehicle are using two completely different networks or frequencies too. Here in the US at least Toyota publishes that they partner exclusively with AT&T and I found nothing about what network(s) they use in Canada.

I'm just here on priuschat to learn and from time to time I'll comment if I think I have something to offer. Sorry I missed the mark entirely and strayed from the subject now that I look back at that. I have the same vehicle and that got me off track.

Best of luck and hope you eventually get your problem identified or some less than painful workaround created.

The dilemma of your situation reminds me of these two movie lines ...

"Let's work the problem, people. Let's not make things worse by guessing." - Apollo 13
"You're gonna need a bigger boat" - Jaws

 

After two years of complaining about the 12v battery problem, are you now willing to listen and follow suggestions about fixing the problem?

 

Occam's Razor time ...

Of course, you get to declare if this is a good suggestion or another stupid one to add to your list but I think you've got issues with one or more of the many accessories you're powering. I think you've got to look at those as the obvious contributors and get your focus off of Toyota for now and all the ways they have to remake the vehicle to give you unlimited accessory power or this latest desire to have it report your battery voltage through the cloud. It's all a diversion from the problem. You've got the test instruments and bluetooth battery monitors that can make light of exactly when your battery voltage falls and rises. And, more importantly you must have the manuals for all your accessories and what they do.

Here's an example from previous statements you've made that struck me about these great mysteries that probably have a simple answer:

Any chance this was your radar detector speaking? I've heard several brands speak phrases just like that. But nowhere have I seen evidence that the Prius does that.

Now you've also said you have a dashcam too ...
At one point over two-years ago you said Toyota installed one for you but then in April 5 2024 you bought another make ... a Viofo A229 Duo dashcam, and had an installer put it in. That was more than 2-years ago and hundreds of posts about battery problems.

Here's a couple quotes I found from other users of that camera who knew their camera installation or configuration was to blame for their battery issues. It sure seems so similar to the timeline and symptoms you've had. Doesn't it? And there's reports of people with alternators and brand-new batteries all having their batteries drained because of a single accessory like this dashcam. Sounds impossible but it isn't.

"Viofo A229 plus draining battery until car doesn't start:
I had my Subaru Forester and Volvo xc40 both professionally hardwired with the viofo A229 plus. The Volvo is fine but the foresters battery keeps dying. The only thing that’s different over the last few weeks is the install of the dash cam. I bought this model specifically for the parking mode due to a safety issue but now my car won’t even start."
----
"I have VIOFO A229 Pro
It works good but the big problem is with the parking mood it stays for just 2 to 4 hours and then goes off on 12V and it takes all the battery power. By the way I have post same post like this couple a months ago but I have been advised to buy a new battery and I bought new and bigger battery 80W and I still have the same problem."

Here's a reply to one of those from a well-meaning person who offers advice on what it might be.

"I wonder if the installer connected your dashcam to two “constant hot” fuse positions. There are two power wires coming from the dashcam with the HK4 wiring kit, one wire goes to constant hot and the other goes to accessory only. If they wired both wires into two constant hot fuse positions, then your Dashcam will never enter parking mode, and it’ll just stay on until the battery dies.

The other possibility is, it’s wired correctly but they may not have selected at which voltage point to shut the dashcam off. There is an inline box in the hardwire kit with a little selector switch for voltage settings. I have mine set to turn off if the battery drops down to 12v, however the lowest setting is 11.8v, which could be enough to drain your battery so it doesn’t start."

another possibility is that they nicked another wire and caused a short, but let’s not get ahead of ourselves."

Hope this helps. I got more, but think this is quite enough.

 

It appears that you are still not ready for good suggestions. I thought maybe you were because you are no longer able to use your NOCO battery charger/maintainer at night as a workaround.

 

I guess you will continue living with the problem until you start listening to good suggestions that are given to you.

 

Toyota manual agrees with you that 5-minutes of driving is sufficient to recharge the 12-volt battery but only if "Auto Power OFF to Conserve Battery" is shown. The owner's manual also references 5-minutes of running the engine of a second rescue vehicle when it's giving your Prius a boost. That's all I found that referenced 5-minutes when it comes to the 12-v battery.

FYI ... while researching that I found other statements from the owner's manual:

When the 12-volt battery is removed or discharged

Information stored in the ECU is cleared. When the 12-volt battery is depleted, have the vehicle inspected at your Toyota dealer.
​

After recharging the 12-volt battery

Have the 12-volt battery inspected at your Toyota dealer as soon as possible. If the 12-volt battery is deteriorating, continued use may cause the 12-volt battery to emit a malodorous gas, which may be detrimental to the health of passengers.
​

To prevent 12-volt battery discharge

• 
  
  
  • Turn off the headlights and the audio system while the hybrid system is off.
  • Turn off any unnecessary electrical components when the vehicle is running at a low speed for an extended period, such as in heavy traffic.

- Charging time may increase

In the following situations, charging time may become longer than normal:
The vehicle is consuming a lot of electricity, for example, when the headlights are on etc.​

 

I'm quite done here. I feel you're the smartest guy in the room but it's because you're continually baiting an audience with ever more spectacular stunts and stealing our time and goodwill in an effort to see if we get the joke. Just your history of 24x7 coolers in the summer and Truckers Ovens that have melted plastic in a GEN3 suggests it's been going on for a long time. I'm sure once you convince Toyota to add a flux capacitor this will subside. Best of luck.

But do want to remind the audience of the brilliance of @Brian1954 when he sight-unseen saved the day in August 2025 when this same tired 12-v litany had a new discussion started under the title "My car has needed a boost for 7 straight days". It's worth a revisit to see what people that try to help can do even when they have no access to the vehicle and share incredible ideas to solve problems. By the way, I do suggest the OP revisit that too for I think you only swapped the 4 AMP fuse and put in a 5 AMP fuse for a NOCO Genius5 charger that was added to support the cooler. Wrong again, the NOCO Genius5 fuse should be a 10 AMP fuse. I still marvel in that call @Brian1954.