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Wait a minute! Are you saying I can't park the car for a month and have a 12v battery that still works? Why wouldn't the system use energy from the traction battery to help keep the 12v fully charged? That seems kind of obvious doesn't it? Those background accessories can't be using much power but over time w/o the traction battery thru a transformer to keep the 12v charged it could def get low.
 

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I had an issue with a 2015 Prius that was very annoying and Toyota did not wish to address it. My wife drove about 2.5 miles to work. After 3 years she started having trouble with the car not starting. We were told by Toyota that she did not drive the car enough for the 12 volt battery to charge and that I needed to get a trickle charger to charger the 12 volt battery while the car was in the garage. I sawon Prius forums that others were having similar issues. This had been our second Prius. We never had any such issues with our 2011 Prius. I started having her carry a small portable jump start kit. I don't think we will have that issue with our R4P.
 

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Wait a minute! Are you saying I can't park the car for a month and have a 12v battery that still works? Why wouldn't the system use energy from the traction battery to help keep the 12v fully charged? That seems kind of obvious doesn't it? Those background accessories can't be using much power but over time w/o the traction battery thru a transformer to keep the 12v charged it could def get low.
The traction battery is not delivering any power to the Hybrid system when the vehicle is in an OFF or ACC state, and it is the Hybrid system that charges the auxiliary (12V) battery. If storing a Hybrid vehicle for 30 days or more, Toyota recommends you disconnect the auxiliary battery.
 

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The traction battery is not delivering any power to the Hybrid system when the vehicle is in an OFF or ACC state, and it is the Hybrid system that charges the auxiliary (12V) battery. If storing a Hybrid vehicle for 30 days or more, Toyota recommends you disconnect the auxiliary battery.
Thank you Tim. Is is sufficient to disconnect just the negative terminal on the 12v battery? A trickle charger is discourged do you believe?
 

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Is this every 2 months ritual only when the car is in storage? Thanks for that, but still not sure why a trickle charger wouldn't be totally fine.
 

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A battery maintainer should work fine as long it is of decent quality so as to prevent over-charging the battery.

My Rav4P is sitting in an airport parking lot now. It will have sat almost 3 weeks when I pick it later this week. I will be very surprised if there are any 12V issues but time will tell.......
 

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Those background accessories can't be using much power but over time w/o the traction battery thru a transformer to keep the 12v charged it could def get low.
FWIW, transformers only work with AC current. The R4P uses a DC-DC converter to charge the 12V battery from the HV battery. A DC-DC converter is similar to an inverter followed by a AC-DC converter but there is no transformer involved.
 

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A battery maintainer should work fine as long it is of decent quality so as to prevent over-charging the battery.

My Rav4P is sitting in an airport parking lot now. It will have sat almost 3 weeks when I pick it later this week. I will be very surprised if there are any 12V issues but time will tell.......
NOCO GENIUS2 should work fine.

NOCO GENIUS2, 2-Amp Fully-Automatic Smart Charger, 6V and 12V Battery Charger, Battery Maintainer, Trickle Charger, and Battery Desulfator with Temperature Compensation https://www.amazon.com/dp/B07W6B987...abc_AQBJPW49RM4DT80S450S?_encoding=UTF8&psc=1
 

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I guess what I need to know is this: does the every two months recommendation ONLY apply when the car is 'in storage', or does it applly all the time even when the car is being driven? If it's the latter that sounds just plain bizarre, and I wonder if it is true for most other recent model cars.
 

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I guess what I need to know is this: does the every two months recommendation ONLY apply when the car is 'in storage', or does it applly all the time even when the car is being driven? If it's the latter that sounds just plain bizarre, and I wonder if it is true for most other recent model cars.
The 12 volt battery is being charged when the car is driven. It should not need as much charging as a standard ICE car because there is no starter load being placed on that battery. There is a small amount of power that is used when the car is parked to run some features such as the communication system (DCM) used to communicate with the app, the ability to use the key fob, the alarm system, etc. For very long storage times, this small load may deplete the 12 volt battery. However, a month should not be enough to deplete the battery. As long as you do not put the car into accessory mode too long or ignition on mode (without being in ready mode), the battery should stay charged enough even with short drives.
 

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Ok, very good. It's largely the same as all other cars i've owned of late, thank you kindly.
Yes, it's pretty much the same as every ICE car on the road. The 12V battery is charged when the vehicle is "running" and is not charged when it's sitting idle. Some BEVs and PHEVs take it a step further and top up the 12V battery every so often even when they're not "running" since there's no engine to worry about. My former Outlander PHEV and current Mustang Mach-E both do that. It's a shame the R4P doesn't, but it really shouldn't matter if you're not putting the car into storage.
 

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Just like every other Toyota Hybrid and Plug-in I have driven, when my R4Prime is in Ready Mode the traction battery powers the dc-dc converter to power the 12v system and charge the 12v battery as needed (as seen in OBD data).
 

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Just like every other Toyota Hybrid and Plug-in I have driven, when my R4Prime is in Ready Mode the traction battery powers the dc-dc converter to power the 12v system and charge the 12v battery as needed (as seen in OBD data).
Is it correct to say as long as the TB has lots of charge remaining, say >=50%, then putting the car in the Ready state will automatically, w/o further action on the operator's part, begins to charge the 12v battery? And, therefore there is no need to park the car in a place where exhaust from a running ICE won't cause a safety concern, since the ICE would not start if there is ample charge in the TB. And if so, does it display how long or when the 12v battery will have completed its SoC top off? The devil is in the details so thanks again for sharing your knowledge! We just got the car a week ago, despite Ida flooding the dealership where it was slate to leave on Thursday, when they go wind of Ida (literally!) and so moved their inventory including my car to higher ground on Tuesday or Wednesday, before the flooding occured.
 

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Is it correct to say as long as the TB has lots of charge remaining, say >=50%, then putting the car in the Ready state will automatically, w/o further action on the operator's part, begins to charge the 12v battery?
Yes.

And, therefore there is no need to park the car in a place where exhaust from a running ICE won't cause a safety concern, since the ICE would not start if there is ample charge in the TB.
No, that is not correct. Any time the car is in Ready mode, the ICE could start. It doesn't need the ICE to charge the 12V battery, but there are other reasons that the ICE might decide to start. So any time the car is in Ready mode, it should be in a place that is safe for exhaust.

And if so, does it display how long or when the 12v battery will have completed its SoC top off?
The 12V battery is not like the high-voltage battery that has a specific "100%" charge target. The DC/DC converter acts just a like an alternator in an ICE vehicle. Any time the car is in Ready mode, about 14 volts is supplied to the 12V system, which powers the accessoreis and charges the 12V battery. It doesn't stop providing that when the 12V battery is "full" any more than an alternator stops generating power in an ICE vehicle. You're overthinking this.
 

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I agree this is a minor issue and I wouldn't be worry it. But an alternator in an ICE does adjust its output current based on the voltage of the 12V battery. The voltage regulator adjusts the field current of the alternator to do this.

On a R4P, I'm sure the DC-DC converter performs similarly and adjusts its output based on what is needed. I don't know exactly how this is done but I imagine there is a PWM adjustment in the DC-DC converter that controls this.

But... 1) there isn't really anything you can do to change it and 2) it seems to work well since I haven't heard of any complaints about 12V batteries being under charged. Some early Leaf models had issues with this but Nissan seems to have improved their algorithms around the 2015 model year and later models don't seem as susceptible to the issue. A few Leaf owners use a 12V battery maintainer but I'd guess it's less than 1% of all owners. I've had my Leaf 4+ years without any trouble with the 12V battery. I'll probably check the battery voltage sometime in the next year or so to see how it's doing but in general I don't worry about it.
 

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I'm sure the DC-DC converter performs similarly and adjusts its output based on what is needed.
Sure, it would have to the TB is only going to supply power if there is a deficit somewhere in the system to supply to, for example the auxilliary battery. I guess the practical application is if you've left the car in the garage for a couple of months okay to open the garage door, 'start' it (put it in Ready mode), and leave for 30min and call it good.
 

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I think all Toyota hybrid/plug-ins DO have a 12v charge target/trigger. I always see 13.7v - 14.1v (OBD data) on the 12v when I starts a trip and the 12v needs tending/topping off. Then it lowers to near 12.5v after it hits target/trigger (assume voltage) a few minutes into my trip if I have been driving daily. I also observed a longer tending/charging trip after I ran the 12v down and had to jump start my R4Prime (x3).

In an ICE vehicle the alternator does not stop when 12v is full because it is always charging and supplying power to 12v systems. Ref; “it (ICE alternator) continually charges the car battery while the car is in motion while also simultaneously operating all the electronic components of the vehicle.” From website; Do You Wonder How the Alternator on Your Car Works?

Just like on Toyota Hybrid/plug-ins, the DC-DC converter is always using traction battery to power the 12v systems and 12v charging system (if needed) when in READY mode.
 
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