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It’s when the green Ready light illuminates on the dash. It means the car is ready to drive. It’s the EV equivalent of the ignition being started.
My 2021 Rav4 prime when sitting in the ignition on, or ready mode, not driving, a message on the dash comes on and says the vehicle will turn off if left on for 10 minutes. How would charging continue if it turns off.
 
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.
2021 R4P in Accessory mode, turned off the vehicle to preserve battery power after about 5 minutes. I run often in EV Mode, and only use HV Mode on the freeways or interstates. About 30 percent of my mileage is local in EV Mode and it can be a week or two between freeway driving in HV mode. Had the system checked at the dealer today, and I believe they just checked the battery and said battery tested Green, and they could not duplicate at this time. I did run yesterday in HV mode for about 2 hours, which may have recharged the 12v battery. I tested the battery, car off last night and the voltage reading was 12.5, which is okay, but I feel it should be closer to 12.7. In looking into battery replacement to see what I would face, the owner's manual says to replace with a ventilated calcium type battery. The Dealer did not know anything off hand about a calcium battery. Further checking, they said only 11 on route from Japan and all are spoken for by California Dealerships. The Dealer here in Ohio, did not know when one could be shipped in. Two questions, does the 12v battery only charge as needed in HV Mode, and what should be the car off sitting voltage, as the dealer would not or could not answer that?
 
2021 R4P in Accessory mode, turned off the vehicle to preserve battery power after about 5 minutes. I run often in EV Mode, and only use HV Mode on the freeways or interstates. About 30 percent of my mileage is local in EV Mode and it can be a week or two between freeway driving in HV mode. Had the system checked at the dealer today, and I believe they just checked the battery and said battery tested Green, and they could not duplicate at this time. I did run yesterday in HV mode for about 2 hours, which may have recharged the 12v battery. I tested the battery, car off last night and the voltage reading was 12.5, which is okay, but I feel it should be closer to 12.7. In looking into battery replacement to see what I would face, the owner's manual says to replace with a ventilated calcium type battery. The Dealer did not know anything off hand about a calcium battery. Further checking, they said only 11 on route from Japan and all are spoken for by California Dealerships. The Dealer here in Ohio, did not know when one could be shipped in. Two questions, does the 12v battery only charge as needed in HV Mode, and what should be the car off sitting voltage, as the dealer would not or could not answer that?
Also the Calcium battery is priced at $1439, therefore can an AGM Battery safely replace the 12v Calcium battery?
 
2021 R4P in Accessory mode, turned off the vehicle to preserve battery power after about 5 minutes. I run often in EV Mode, and only use HV Mode on the freeways or interstates. About 30 percent of my mileage is local in EV Mode and it can be a week or two between freeway driving in HV mode. Had the system checked at the dealer today, and I believe they just checked the battery and said battery tested Green, and they could not duplicate at this time. I did run yesterday in HV mode for about 2 hours, which may have recharged the 12v battery. I tested the battery, car off last night and the voltage reading was 12.5, which is okay, but I feel it should be closer to 12.7. In looking into battery replacement to see what I would face, the owner's manual says to replace with a ventilated calcium type battery. The Dealer did not know anything off hand about a calcium battery. Further checking, they said only 11 on route from Japan and all are spoken for by California Dealerships. The Dealer here in Ohio, did not know when one could be shipped in. Two questions, does the 12v battery only charge as needed in HV Mode, and what should be the car off sitting voltage, as the dealer would not or could not answer that?
Also, I do drive my vehicle at least three to six times a week, but often that is in EV mode.
 
This message is probably the message that happens if you have not been driving for almost an hour. You get a similar message if you park and open the driver door without turning the car off. This is to ensure that you do not unintentionally leave the car on where the engine might come on and cause carbon monoxide to accumulate.

The 12 volt battery is always being maintained when the car is in READY mode. This means that no matter whether the engine is on or off, EV mode or HV mode, the battery is being maintained. 12.5 volts when off is perfectly normal. The textbook voltage of a fully charged 12 volt lead acid battery is 12.6 volts. However, there is some battery drain that happens after the car is shut off. This will lower the battery voltage lower than the textbook value. In addition, the battery voltage will go down with age.

Calcium battery - have no idea what this means. The battery is a standard flooded lead-acid battery. No need to buy the imported Toyota battery.
The Manual definitely says Calcium battery. If you google, they are now being used in many Electric vehicles as the accessory battery. Suppose to last longer and more maintenance free as they loose almost no electrolyte over a long period. Toyota started using them in the Primes built in Japan, which mine was.
I had been driving the car for over an hour, which should have charged the battery, yet without getting out, I shut it off and then decided to listen to music as I waited. Put it on Accessory mode, and about 5 minutes later I got the message shut off the vehicle to safe battery power. Tried again to run it and it shut off again in 1 minute. I ran the car coming home for another hour before checking the battery with a tester, that is when I got the 12.5 volt reading. The Dealer did a check, but all they told me was the battery had a green light and they could not get it to do the shut down in Accessory mode.
 
Accessory mode always shuts off after a short period of time. This does not indicate the battery is low. The Prime typically does not have a problem with low 12 volt battery because in addition to being maintained any time the car is in READY mode, it is also maintained when the traction battery is being actively charged using an EVSE. Accessory mode should not be used for any length of time. It is better to just put the car in READY mode and turn off as many accessories as you can. The highest usage will come from the HVAC system.

In looking into calcium battery, it appears that calcium is added to a lead-acid battery to help make it give off less gasses. This is apparently typical of most "maintenance free" lead acid batteries that are used in cars today. I think the manual specifies this because the battery is located in the passenger compartment. However, I would guess that almost any battery that is currently available (possibly not including deep cycle batteries) are "maintenance free", indicating they probably use calcium.
Yes, I know it shuts off over time in Accessory, but not usually in 5 minutes. Then I gave it a minute and and restarted the accessory mode and it shut of in one minute. Both times a message on the dash said: turning off the vehicle to preserve battery power. I had not seen that message before and had used accessory for at least 10 minutes in the past.
 
That message comes up when accessory mode is automatically shut off. I am not sure how the car decides to use different times to shut off.
Neither did the dealer. They convinced me I should have the charging system checked to be sure all was ok. Did that for $95 and they basically said the battery was ok, and not much else. I just filled out a answer to a Toyota evaluation as unsatisfactory. They also had no idea what a Calcium Type Battery was.
 
Glad to see there are recent additions to this thread. I didn't know what I was doing and ran down the 12v battery to 5.9v and now it won't charge up to over 12.2 (the car is giving it 14v as it should). The dealer wants to sell me a battery. Whether I get one from them or Costco, should I get a new battery?
Prime or Hybrid? How much does the Dealer Battery cost? Be sure to get a ventilated battery and rehook up the drain tube. If Prime, buy a replacement battery locally, try to match the original the best you can. If Hybrid, compare with the dealer price, and if you always service at the dealer, consider the warranty.
 
In further research with the dealership, They say if you replace the Rav4 Prime 12 volt battery with a standard lead acid battery, in a short period the system will trigger warning lights. Diehard has an AGM battery, ventilated that they say will replace the Calcium battery in the Prime. Attached is a very good explanation of battery types: What are AGM, EFB and calcium batteries - and why would you need one? | RAC WA
What's an AGM battery, what's an EFB battery - and more importantly, what's the difference?
Here's what they are, how they work and why you might need one.
What is an AGM battery?
In technical terms AGM stands for Absorbed Glass Mat. An AGM battery is different to regular batteries because the electrolyte liquid (battery acid) is absorbed into the glass mats like a sponge instead of the sulphuric acid being free floating as in a conventional battery.
Why would I need an AGM battery?
Many of the technologies and accessories now included in modern cars put extra demands on their batteries. AGM batteries are designed to cope with these higher energy drains and demands. For example, the Stop-Start technology featured in many modern vehicles requires a battery with a higher output and AGM batteries excel in this regard. Where Stop-Start is enabled, the vehicle’s engine cuts out instead of idling when the vehicle is stationary in order to save fuel. AGM batteries ensure that when your car has stopped, it will rapidly and seamlessly start again when you’re ready to move off.
AGM deep cycle batteries are also safe to install inside the cabin of a vehicle to run accessories, as they don’t release harmful gases. Some AGMs are dual purpose so they can also start a vehicle's engine
If your car currently has an AGM battery, then it’s important that you replace it with an AGM battery to ensure your car’s health is maintained.
AGMs have several advantages:
  • AGMs produce higher amp power output for the same size of calcium battery, meeting the increasing demands of car electrics and technologies.
  • AGMs are better suited to the modern car charging system.
  • Dual-purpose AGMs can function as both a starting battery and as an accessory battery, so they can support a multitude of new accessories and car technologies.
  • Deep-cycle AGMs are safer to install in the passenger compartments of vehicles because they’re sealed and don’t produce harmful fumes or gases.
  • Because an AGM is fully sealed it is also maintenance free.
What is an EFB battery?
An enhanced flooded battery (EFB) can also be used in cars that feature Stop-Start technology. It is considered an entry level battery for use in cars with this technology. EFBs are wet-filled and similar to standard flooded batteries, however, there are differences that give these batteries enhanced cycling abilities and improved charge acceptance. This means the battery recovers more quickly, as its application needs to handle heavy-duty, cyclic, Start-Stop applications.
Does my car need an EFB battery?
Your vehicle will only require an EFB battery if it currently has one. For example, vehicles with Stop-Start technology may use one of these batteries. If in doubt, check with us before ordering a new battery.
Both AGM and EFB batteries are designed for the frequent cycling required when a vehicle is equipped with Stop-Start technology. Vehicle owners new to the Stop-Start feature may be concerned about the impacts of it on the battery, however, batteries that are required for this technology to function correctly are built to tolerate constant stopping and starting. It is also why replacing your battery with the correct type is essential to maintaining its performance.
What is a calcium battery?
Calcium batteries are lead acid batteries that have small amounts of calcium added to the plates. Battery plates are made from lead alloy, however a pure lead grid structure is not strong enough to hold the battery material vertically, which is why other properties must be added to increase the mechanical strength of the lead. The two most common alloyed metals used are antimony and calcium.
What the added antimony does is increase the electrical resistance of the alloys and subsequently the grids produced from them. These grids require a lot of electrical conduction for optimum performance but when compared to calcium, they are roughly 3-10 per cent less conductive.
In positive grids containing antimony, the process of conductivity means some of the antimony is released from the corrosive product of the grid and transferred to the negative plate. This action during charging promotes the breakdown of water and generation of hydrogen. This gassing phenomenon causes water loss in other batteries, resulting in the need to periodically add water to maintain the battery’s condition. RAC Batteries are fully sealed and maintenance free.
Does my car need a calcium battery?
The benefits of replacing antimony in the plates include improved resistance to corrosion, no excessive gassing and reduced water usage. The use of calcium also cuts down on the loss of charge from the internal chemical reactions required in the lead-antimony self-discharge. This means they are less likely to be affected by extreme weather conditions and higher charge rates. Many modern cars now use them to cope with the higher power demand from engines and accessories.
Calcium batteries are regarded as low maintenance, as they practically do not evaporate the electrolyte and therefore will not need water added.
Despite the upsides, calcium batteries should still be charged with an appropriate battery charger if not used regularly. If you’re going to use it as a deep cycle battery, it’s best to hook up a charger designed for calcium batteries to get the most out of its lifespan.
 
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