HV Battery magically has a charge... How???

sounds like a malfunctioning charge meter. i would bring it in to check for trouble codes

 

Have you ever changed your 12V? All of those lights on the right hand side seem to say either your 12V is low or you have a loose 12V cable.


iPad ? Pro

 

THIS.
And.....the circuitry that detects the State Of Charge in the HV battery is not perfect.
It is not unusual for it to vary some like you have noticed.
But maybe not that much.

 

Agreed. Check the 12V and its connections. That might explain the erroneous battery indicator and those warning lights. Those caught my attention right away.

 

In my opinion, the Toyota battery is the best one. If your battery lasted eight years, why would you change brands?

 

Even if you never plug it in, part of the HV battery is still used more or less like the much smaller one in a conventional hybrid model.
But it will never come close to being "fully charged"......I assume.
You should not be purposely trying to force the car to do something that it doesn't want to do......but some owners never quite understand that.

So.....if your 12 V really is the original, you should change that first.
And check the connections at the OTHER end of the main cables.
Be sure that your new one is fully charged and then check the charging voltage while running.

I would think that it would be good to plug it in and fully charge the battery every few months at least.
Others will no doubt chime in and tell me how wrong I am.

 

A degraded 12V battery can lead to many different issues, the least of which is not being able to start. The PiP is pretty much one big rolling computer (as are pretty much all Toyota/Lexus hybrids BTW), so a low 12V would affect sensors as well as other ECUs that rely on it's initial state. I used to use a technique called "stacking" on the PiP by keeping it in HV mode and liberally using brakes and lots of gas pedal manipulation to force it to store power. You may have inadvertently been stacking your PiP and when parked, the low 12V battery may have caused one of the ECUs to "lose" its stored EV state. The 12V isn't just used to power up the car, but it also runs a couple of post power off routines like depressurization of the brakes, turn off the DC/DC converter and run fans. This may have run the 12V to a limit where it caused an internal reset if a certain routine didn't finish. As your car ages these ECUs also age and on occasion they may become more sensitive to voltage changes. Your situation of constantly trying to restart seems to have finally tricked the DC/DC converter (which has its own ECU BTW) to finally kick on by giving multiple charges just out of range of a full restart.

But "@sam spade 2" indicated you might want to charge it on occasion because that also turns on the DC/DC converter to charge the 12V as well.

 

Sounds to me like the 12V battery is failing, leading to failed starts and ECU memory loss, so it's reporting inaccurate range. You say it was showing a range of 9 miles, but could you actually drive 9 miles in EV mode? I suspect not.

 

@ThatOddMan : What is the current state of your car fix? Did you change the 12V battery? Did it fix the issue?
I am having the EXACT same issue since last month for my PiP(2013). Mine also the Original 12V battery came with the car, never changed. I just want to learn from you before replacing that battery. Any updates from your fix? Thank you in advance.
BTW, thank you for all other forum members for sharing their thoughts around the issue.

Mine shows 9 EV miles in the morning out of nowhere, it runs all these EV miles too.
But as ThatOddMan's first video shows above, the xmas lights will keep for a good 10 min before the READY indicator gets on. I need to keep pushing the start button several times(as shown in the video above) to get the READY.
Update: Looks like @ThatOddMan has changed his 12V battery but still having the SAME issue as of two weeks back

 

either way, it would be smart to change a 9 year old battery before you're left stranded, or carry a jump pack

 

I think you are right.. regardless, I should for for 12V make-over. Thanks Sir @bisco for that safe hint.

 

Makes no difference what experience anyone else has had.
At 9 years old, you NEED a new battery.

 

I think, if the dash lights come on intermittently and the dash lights clear after a few cycles of - Power button On/Off -, that, unless there are permanent (Diagnostic Trouble Code) DTC's set already, you both, @ThatOddMan and @SlidingBike might want to get the DTC codes as they are set (with the dash lights on).
And, I'm not saying there aren't already permanent DTC codes set in both of your cars. So, if it were happening to me, that would be the first thing I'd do, after I checked the 12volt batteries health with at very least a multimeter / voltmeter with the car Off, than in (Accessory - one Push of the Power button without pressing the brake pedal), than ( Ignition On - Press the Power button twice without pressing the brake pedal) , getting voltage readings for all three ...... You can go further by switching on the headlights, turning on the heater and or A/C and checking the voltage for each.

DTC in cases like these will typically get much better results from those that know them (DTC's) best.
Without DTC's everyone is giving educated guesses.

 

Update: @ThatOddMan has replied me that the replacement of 12V battery has fixed his issue. Now I am shopping around for the battery. Local Toyota Dealer doesnt have them in stock(No ETA of getting them), going to drive to another dealer bit far, its part# is 28800-21171, costs around $260(if I give my old battery back to them). Thanks.

 

While Prius batteries are often scarce, there is no reason that your new one MUST come from a Toyota dealer.
Use the phone or the Internet. Check nearby auto parts stores, battery stores, tire stores and even WalMart.
You might save some time and money.

 

Update: Replaced the 12V battery with Toyota (TruStart brand) Batt (total $272 with CA tax). Replaced it by myself using a youtube video. So far, the issue is not occuring again(will watch for it for few more days). All good.
Thanks @ThatOddMan for well documenting the issue with videos and with your posting here, it really helped me. Thanks others for their right suggestion to replace the 12V brick.

Side note: Also got my Cat Converter Shield installed (total cost $320 cash):

 

I just replaced my 3rd 12 volt and the hybrid battery is ant fully charged it’s down 2 bars. I’m not sure what is causing the 12 volts to drain. I hAve 94,000 miles on a 2012 prius V.