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2021 Rav4 Prime XSE Pro Audio/Dynamic Nav/Weather Packages Build date: June 2021
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When the prime is placed in My Room mode, the 12v Accessory battery is charged
Was this written somewhere? I looked and never saw any direct statements to this effect, It maybe begs the question why was this not alluded to when they gave the precautionary statement re the 12v battery discharging after prolonged periods of non-use and not being able to start the car, and I think their example was 2 months. I don't think I read the manual suggesting to connect the charger, then after sufficient charge activate My Room mode to help restore the 12v battery?
 

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I doubt you'll find anything in the manual as a strategy but it has to be the case. When you're in My Room Mode all of the accessories are live, and if it didn't charge the battery you'd suck it down in no time.
But...if all accessories are turned off, which was the recommendation I believe, why is it assumed the 12v battery is charging when there is little to no demand? Is it possible then that this strategy only maintains the 12v battery when accessories are actually turned on?
 

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Let's say the 12v battery happens to be discharged to say within 30% of too low to be able to start the car. We now, with the traction battery charger connected, activate My Room mode. All accessories are OFF. I guess it is being suggested the 12v battery is now being charged as a consequence of being in My Room mode. Is this allegedly because it is designed to anticipate accessories will be used so will attempt to 'top off' the 12v battery? If this is what is being said here, I'm puzzled why Toyota failedl to suggest this maneuver for when the car has sat for 2 months or more and the hybrid system won't start because of a discharged 12v battery?
 

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Makes sense to me thanks. For my 787-10 Dreamliner (2016 BMW R1200RT😅) I replace the 12v battery every 2-3 years regardless of its condition as I don't care to be stranded ever due to a dead battery! Sounds like a good idea w/ R4P as well, maybe every 2 years. In the mean time if the car has sat for several weeks, which it never is, we can to the My Room charge routine. It would be great if someone could verify this actually works!

Cheers
 

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... it will start charging/topping-off the 12v..... when you plug in the EVSE and start a charging session (as see in video below).
This implies there is no need to go into the MyRoom ritual, correct? If that's so I don't understand where any problem lies beyond just as you say the puny battery and even then it seems like more of an issue of durability of battery since we're all plugging in the EVSE regularly.
 

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As previously mentioned, the Prime does in fact charge the 12v Aux battery when the Prime is plugged in AND charging.
Is it possible w/ your gizmo to leave the EVSE attached for as many hours as you can live with after the charge is complete to monitor for voltage loss during that time? There is a contention that keeping the EVSE attached after charging the car that parasitic draw will commence, but we have no idea how much and for what period of time. Thanks in advance if you can do this!
 

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I'll try to get some data of the Prime plugged in for a long period of time with no charging going on and see what that says.

dp
[/QUOTE]
Thanks so much for that it will add to the useful dbase for sure! BTW, what gizmo is that? Monitoring electrical information seems like it could be worth if for me!
 

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I don't see why not. In theory it should be the same voltage but with some minor losses. It may be worth comparing if there's a measurable difference between the reading at the battery terminals and the reading at the jump terminals.
Can I just connect the multimeter to the cigarette lighter w/ an appropriate adapter? I would like to test the rate of discharge after the car has just finished charging but with the charger still connected.
 

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I would like to add: checking the rate of discharge right after a full charge will yield a false result, because there would be a steady discharge even if there was no load at all. The actual voltage should be stable after 24h. But unless you disconnect the 12v battery, this is not really doable.

dp
I'd like to measure battery voltage immediately upon charge completion, then retest perhaps every few hours or so while leaving the charging cable connected the whole time. What is the source of the steady discharge you refer to, when does it commence, that you're suggesting slows down or stabilizes after 24h? Is the battery the easiest/quickest unswitched place to connect to 12v?
 

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Hey Folks, best/easiest spot to connect a multimeter to test 12v charge status with the car off? Would the + jumper cable connector in the fuse box be good?
 

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Well...interesting findings that I don't know what to make of! Here's what I did:

The car was at zero Soc for the TB when I did this short experiment, ambient temp 37F, doors locked, key fob NOT disabled. Car was built June 2021.

Prior to connecting the OEM 120v EVSE the 12v battery voltage was 12.43v
Immediately after connecting to charge: 12.63v
1h after charge complete but w/ EVSE connected: 12.39v
3h after charge completed w/ EVSE connected: 12.55v
6h after charge completed w/ EVSE connected: 12.47v
NOTE: multimeter remains connected during this time, however turned OFF except when checking voltage.

I needed to use the car so stopped the test earlier than planned. Took a short trip, returned then reconnected the EVSE to top off the charge which only took an hour or so.

Now here's where it gets weird! After re-charging to complete, I disconnected the EVSE. I reconnected the multimeter and again kept if OFF except when checking voltage.

12v battery now: 12.29v. Hmm, okay whatever! Ambient now around the same, 37F.
1h later: 12.17v
4h later my wife hears a funning hum coming from the car when she went out into the garage for something. I went out, retested voltages, now 12.09v. I disconnected the multimeter and the hum stops. Apparently it did not like keeping the MM connected even though it's absolutely turned off--at least the switch is off and display is blank.
This morning I just checked: 12.07v. I hope the car starts :oops:

Apparently keeping the MM connected is not a good thing even though it is turned off. Hard to draw too many conclusions here but it certainly seems like keeping the EVSE connected after charging completes demonstrated at some level 12v battery voltage actually went up, though dropped down slightly at the 6h post charge complete check. If the car starts I will try the test leg where we disconnect the EVSE and check 12v battery after charging complete, except will disconnect the MM as well except when testing.

Cheers
 

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Modern cars do a self test of the fuel system by pressurizing the fuel tank. You may have heard that process. It kind of freaked me out the first time I heard my 2018 CRV doing it.
The humming being related to the MM could well have been a red herring.
 

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I don't quite understand the great concern on the battery voltage. After three days with no activity on the car, my battery is at 11.5V. I am not concerned. A full battery is 12.6v. When I see 10v, I will be concerned. When I start (ready) the machine, the battery voltage will go to 14.3v or.4. Parasitic draw is there, and that is a fact. I believe that as long as it is not an external draw the car will function just fine. My rav is 11 months old and has sat for up to a week with no external connection and starts just fine. FWI
I guess the concern has come from a few here w/ dead batteries that were not very old. It is great to know 11.5V is not a problem with this car. Several articles I read suggest that is almost too low to start 'a car' with.
 
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