[gregeusa]

another update, did a short experiment today:

EV battery was up to 41 miles range
took off, and it went down to 40 on EV, then changed to HV auto
went to the store, and back, just a few miles.

ev range stayed at 40
and using the power flow display, I saw that any regen available did indeed go to the battery, i.e. in this mode the system did INDEED charge the battery while it was over 80%, and very close to full (1 mile away)

Also as i was driving (stop and go, surface streets and moderate hills all the way), there were times the ICE did charge the battery.

So, the "system" is not as simple as one would believe.

AND there are definitely modes where the traction battery will be charged when it is OVER 80%...

So, I'm sure the manual is trying to make a somewhat "simple" description of what goes on, but quoting the manual chapter and verse and saying it is immutable truth and inalterable rules, well, it just is not so.

I'll do some more playing around, but clearly the algorithm is not a simple 80% or not rule..

Greg

 

[CoffeeBear]

another update, did a short experiment today:

EV battery was up to 41 miles range
took off, and it went down to 40 on EV, then changed to HV auto
went to the store, and back, just a few miles.

ev range stayed at 40
and using the power flow display, I saw that any regen available did indeed go to the battery, i.e. in this mode the system did INDEED charge the battery while it was over 80%, and very close to full (1 mile away)

Also as i was driving (stop and go, surface streets and moderate hills all the way), there were times the ICE did charge the battery.

So, the "system" is not as simple as one would believe.

AND there are definitely modes where the traction battery will be charged when it is OVER 80%...

So, I'm sure the manual is trying to make a somewhat "simple" description of what goes on, but quoting the manual chapter and verse and saying it is immutable truth and inalterable rules, well, it just is not so.

I'll do some more playing around, but clearly the algorithm is not a simple 80% or not rule..

Greg

I can't tell if you are referring to charge mode or simply situations where the ICE is charging the battery. I'm fairly certain you can only use charge mode up to 80%. This does not preclude the ICE from charging the battery in HV mode beyond that point but I'm not 100% sure what factors will determine that. how do you know what percentage you are at during these tests? you can't really rely on the miles left "guess-o-meter".

 

[wscan]

So, I'm sure the manual is trying to make a somewhat "simple" description of what goes on, but quoting the manual chapter and verse and saying it is immutable truth and inalterable rules, well, it just is not so.

The manual says that charge mode stops at 80%. It does not say anywhere that I am aware of that the ICE does not charge the battery above 80% nor does it say that regen does not occur above 80%. The car does charge the battery above 80% using both regen and ICE when the ICE is running. The algorithms decide when to charge and not charge the battery. I assume the Prime works like other Toyota hybrids where regen will charge the battery to 100% of the Toyota limited maximum charge (90% SOC) as needed. However as the battery approaches that maximum, the charge from regen is reduced and the car kicks in engine braking. Most of the time in the Prime, you don't get to the maximum charge point since the battery is so big compared to other hybrids.

 

[gregeusa]

Again, the manual is not to the level of detail of all the things I am seeing... I don't care about the manual, I care about what the car does. We have gone beyond the manual, and to keep quoting it at this point is useless in my opinion.

I did clearly state that the car showed regen on the screen, so that is data, not speculation.

All I was stating is that the system will let the ice/regen charge the battery when the battery is over 80%...

 

[Steve_j]

All I was stating is that the system will let the ice/regen charge the battery when the battery is over 80%...

Is that "80%" 80% of the physical capacity of the battery or 80% of whatever maximum charge the computer allows for the battery?

 

[mejmea]

I can contribute some data.

Last fall we traveled from our house about 45-50ish miles to the city for a wedding. My plan was to have the battery fully charged, drive to the city in HV mode, and then be able to use the battery for in city/traffic-y driving. Once we got on the highway however, I noticed that the charge level kept dropping even though I was in HV mode. Eventually it stopped at about 80% (as estimated based on the charge bar as well as the number of EV miles that were ultimately available). I don't remember it being especially hot or anything but the climate control system/AC was no doubt running to some extent.

So, under those circumstances at least, the system was unable to maintain a "full" (i.e., Toyota's definition of full) charge in the battery. I remember it well because it surprised me...

 

[mejmea]

Is that "80%" 80% of the physical capacity of the battery or 80% of whatever maximum charge the computer allows for the battery?

To the best of my knowledge that is 80% as indicated on the in-vehicle gauge/in the Toyota app. That translates to around 63% actual SOC based on measurements I've made on my R4P.

 

[gregeusa]

yeah, I'm keeping it to the displayed range in miles...

I surely do not want to start complicating this with the ACTUAL SOC, unless I can read that directly (i apparently do have the hardware)...

I'm just concentrating on under what conditions I can increase the traction battery charge without external "charger"

so to answer the question posed to me: the 80% I referred to is 80% of the max EV range I can get as displayed on the screen in the car.

So in my car, the max range is usually 42 or 41 miles... under HV running, I see the battery being recharged at OVER 80% charge, i.e. which is about 27 miles of range indicated...

my last test, the system was still putting electrons back into the battery at 40 miles EV range, and i did not drive to see if it climbed above that.

apparently there is a way to mitigate the "bleeding" of the HV battery at a charge state/range OVER the 80% that is constantly being referred to.

More experiments on the way.

 

[espos4]

another update, did a short experiment today:

EV battery was up to 41 miles range
took off, and it went down to 40 on EV, then changed to HV auto
went to the store, and back, just a few miles.

ev range stayed at 40
and using the power flow display, I saw that any regen available did indeed go to the battery, i.e. in this mode the system did INDEED charge the battery while it was over 80%, and very close to full (1 mile away)

Also as i was driving (stop and go, surface streets and moderate hills all the way), there were times the ICE did charge the battery.

So, the "system" is not as simple as one would believe.

AND there are definitely modes where the traction battery will be charged when it is OVER 80%...

So, I'm sure the manual is trying to make a somewhat "simple" description of what goes on, but quoting the manual chapter and verse and saying it is immutable truth and inalterable rules, well, it just is not so.

I'll do some more playing around, but clearly the algorithm is not a simple 80% or not rule..

Greg

There’s no HV Auto mode.
only HV or EV Auto.

which mode did you use?

also on short cold start HV trips, the engine run time is relatively longer so EV miles won’t drop much when starting at a full EVSE charge.

Fact is the traction battery will indeed drop down to the 80% when starting a hv trip with a full battery.

I’m going on 3+ years and 45,000 miles. It does it EVERY time.

 

[Whereitis]

Yesterday we made a 5 hour trip with a planned stop about half way. When we arrived at our first stop , I noticed I never put the car into HV mode before I got on the highway . Here I am on a week+ trip with 0 EV miles available. I didn’t feel comfortable at zero, so there goes my plan to never need to use a charging station while en-route. Of course I felt stupid.

Then I remembered the HV Charge mode. I had to look up the procedure in the manual, but I put into charge mode for the 2nd half of the trip. I was surprised how quickly it charged. I didn’t time it, but I would guess it fully charged in about 30-45 minutes. Probably not the most efficient way to charge, but I was glad the capability was there.

I discovered CHG mode from a well-done YouTube video discussing all the RAV4 Prime's features. Charge Mode is awesome! It's the mode that gives you total control over the HV battery's state of charge. Once discovered, I started playing with it and found you typically add 1 mile of EV range for every 3 miles driven in CHG mode.

 

[Whereitis]

As others have said, a full 12 hrs plugged into 110v at home will get it up to 42 EV miles. Putting it into HV mode as soon as I leave home, it will slowly drop to 34 and stay there. Running in Charge mode (if EV charge has dropped lower by running in EV mode) will restore EV range to a maximum of 34 miles, or about 80% of full charge. It seems very consistent, and it's certainly adequate.

Although one could always wish for more, I don't know another PHEV on the market today that offers as much as the R4P, much less more. I would love a PHEV that has the same 450 miles of HV range (or even more) plus 100+ miles of EV range. I'd bet PHEVs that can do that will be on the market within 10 years or less.

 

[FLYNZ4]

As others have said, a full 12 hrs plugged into 110v at home will get it up to 42 EV miles. Putting it into HV mode as soon as I leave home, it will slowly drop to 34 and stay there. Running in Charge mode (if EV charge has dropped lower by running in EV mode) will restore EV range to a maximum of 34 miles, or about 80% of full charge. It seems very consistent, and it's certainly adequate.

Although one could always wish for more, I don't know another PHEV on the market today that offers as much as the R4P, much less more. I would love a PHEV that has the same 450 miles of HV range (or even more) plus 100+ miles of EV range. I'd bet PHEVs that can do that will be on the market within 10 years or less.

I suspect you are correct... but probably much less than 10 years. For my daily use, I will likely not use even half of the 42 miles around town. Our frequent longer trips are well outside of EV range so those will be made in HV mode.

In summary, I suspect most times I drive will be pure EV, but I expect most miles will be HV. Hence an EV without range anxiety.

 

[mejmea]

I wonder if the reason the system only charges to 80% when in charge mode could be related to the typical lithium battery charging strategy/cycle. Specifically, the initial part (and majority of) the charging cycle is typically done at constant current with the cell voltage floating upwards as they charge. The final part of the cycle typically changes to a constant voltage strategy when the cells reach the target final voltage. i.e., at that point the current drops over time while the voltage remains constant to finish the charge cycle.

It seems possible that, due to engineering and/or marketing constraints, the on-board (engine driven) charging components/circuits were not designed to handle the entire charging cycle.

It also seems possible that limiting the charge mode charge level to 80% is a way of consciously preventing people from using it to stay at a high SOC continuously for battery longevity/warranty reasons.

(And, just to avoid any confusion or misunderstanding, I do understand that (all of the above aside) the system limits the actual SOC to between approximately 14% to 90%, presumably also for longevity/warranty reasons.)

I'm not sure anyone cares but me as it it a bit of an esoteric point, but I have done a lot more thinking, number crunching, and learning on this point and have rejected the above ideas. I think the actual answer is much simpler (think Occam's Razor) - more on that below

Without boring people with too much detail:

• I've calculated the average power required to charge the battery from 0-80%, using charge mode while driving at roughly 60 mph, at just under 10 hp (around 7300W to be specific). This is based on reported charging times of around 1.25 hours while driving at that speed and using charge mode. While I wouldn't fight too hard about the exact number because there are some assumptions/simplifications in there, that value doesn't seem unreasonable to me.
• That amount of power is far less than what MG1 is capable of, so there isn't a limitation in that regard.
• That amount of power is also far less than what can be put into the battery via regenerative braking or pulled out of it under acceleration, so component sizing (wire gauge and such) can't really be the limitation.

Ultimately, my personal conclusion is that the real reason Charge Mode will only let you go to 80% is that if you are operating in hybrid mode, Toyota wants you to have some headroom in the battery to allow for optimal hybrid operation. It is true that if you are in a situation where you can regenerate a lot (e.g., going down a long hill) they will let you completely charge the battery, but at the bottom of the hill they will start pulling it right down again to provide that headroom. While I have not ever owned a RAV4 hybrid (i.e., not a Prime), it seems to be reported that those owners typically don't see full charge on their battery gauges either (unless they go down a long hill) but rather see a max of maybe 6 out of 8 bars or so. which is consistent with the theory.

I obviously can't state the above as fact since I don't have inside knowledge but, going back to Occam's Razor...

 

[Dimitrij]

I'm not sure anyone cares but me as it it a bit of an esoteric point, but I have done a lot more thinking, number crunching, and learning on this point and have rejected the above ideas. I think the actual answer is much simpler (think Occam's Razor) - more on that below

Without boring people with too much detail:

• I've calculated the average power required to charge the battery from 0-80%, using charge mode while driving at roughly 60 mph, at just under 10 hp (around 7300W to be specific). This is based on reported charging times of around 1.25 hours while driving at that speed and using charge mode. While I wouldn't fight too hard about the exact number because there are some assumptions/simplifications in there, that value doesn't seem unreasonable to me.
• That amount of power is far less than what MG1 is capable of, so there isn't a limitation in that regard.
• That amount of power is also far less than what can be put into the battery via regenerative braking or pulled out of it under acceleration, so component sizing (wire gauge and such) can't really be the limitation.

Ultimately, my personal conclusion is that the real reason Charge Mode will only let you go to 80% is that if you are operating in hybrid mode, Toyota wants you to have some headroom in the battery to allow for optimal hybrid operation. It is true that if you are in a situation where you can regenerate a lot (e.g., going down a long hill) they will let you completely charge the battery, but at the bottom of the hill they will start pulling it right down again to provide that headroom. While I have not ever owned a RAV4 hybrid (i.e., not a Prime), it seems to be reported that those owners typically don't see full charge on their battery gauges either (unless they go down a long hill) but rather see a max of maybe 6 out of 8 bars or so. which is consistent with the theory.

I obviously can't state the above as fact since I don't have inside knowledge but, going back to Occam's Razor...

I am not sure I am following, but I do love me a good empirical engineering paper .

 

[Steve_j]

Ultimately, my personal conclusion is that the real reason Charge Mode will only let you go to 80% is that if you are operating in hybrid mode, Toyota wants you to have some headroom in the battery to allow for optimal hybrid operation. It is true that if you are in a situation where you can regenerate a lot (e.g., going down a long hill) they will let you completely charge the battery, but at the bottom of the hill they will start pulling it right down again to provide that headroom. While I have not ever owned a RAV4 hybrid (i.e., not a Prime), it seems to be reported that those owners typically don't see full charge on their battery gauges either (unless they go down a long hill) but rather see a max of maybe 6 out of 8 bars or so. which is consistent with the theory.

I obviously can't state the above as fact since I don't have inside knowledge but, going back to Occam's Razor...

That is one reason but there are also several additional valid reasons.

In Toyota hybrids, the traction battery (usually a nickel-metal hydride or lithium-ion battery) is rarely fully charged due to several key design and operational principles aimed at maximizing battery life, efficiency, and performance. Here’s why:

### 1. Battery Longevity
- Avoiding Extreme States: Lithium-ion and NiMH batteries degrade faster when kept at very high or very low states of charge (SoC). Toyota intentionally keeps the battery in a mid-range charge (typically 40-80%) to minimize stress on the cells.
- Reduced Chemical Degradation: High charge levels increase internal resistance and heat generation, accelerating capacity loss. By avoiding full charge, Toyota extends the battery's lifespan.

### 2. Regenerative Braking Optimization
- Buffer for Energy Recapture: Hybrids rely on regenerative braking to recharge the battery. If the battery were fully charged, there would be no capacity to store this recaptured energy, wasting efficiency opportunities.
- Dynamic Charge Management: The system constantly adjusts the charge level to ensure there’s always room for regenerative braking energy.

### 3. Power Delivery & Performance
- Instant Power Availability: Hybrid batteries need to provide quick bursts of power (e.g., for acceleration) and absorb energy (e.g., during braking). A mid-range SoC allows for optimal discharge and charge rates.
- Avoiding Voltage Sag: Fully charged batteries experience voltage drop under heavy loads, while partially charged ones maintain more stable performance.

### 4. Thermal Management
- Heat Reduction: High states of charge generate more heat during operation. By limiting the maximum charge, Toyota reduces thermal stress, which is critical for long-term reliability.

### 5. Software Control Strategy
- Toyota’s Hybrid System Logic: The vehicle’s power control unit (PCU) actively manages the battery’s charge level based on driving conditions, ensuring it never stays at extremes for long.

### Result?

• Toyota hybrid batteries often last 200,000+ miles with minimal degradation because of this conservative charge management.
• Unlike EVs, which sometimes charge to 100% for maximum range, hybrids prioritize cycle life over capacity utilization.

 

[mejmea]

@Dimitrij

Lol. Basically my conclusion is that there are no hardware reasons that the system on the vehicle could not charge the battery to 100%. On the other hand, if the battery is charged to 100%, you cannot really have an effective hybrid vehicle.

So, when you are operating as hybrid (which you inherently are when operating in charge mode), the system wants to leave enough headroom in the battery to operate effectively.

I suppose Toyota could they have implemented a bifurcated charge mode (i.e., "Choose option 1 if you intend to operate as a pure EV after using Charge Mode, choose option 2 if you intend to operate as a hybrid.") and adjusted the final charge level accordingly, but that could just cause more confusion and/or problems down the road I suppose.

Again, this is all technically speculation (albeit what I'd like to think is educated speculation...)

 

[Steve_j]

@Dimitrij

Lol. Basically my conclusion is that there are no hardware reasons that the system on the vehicle could not charge the battery to 100%. On the other hand, if the battery is charged to 100%, you cannot really have an effective hybrid vehicle.

So, when you are operating as hybrid (which you inherently are when operating in charge mode), the system wants to leave enough headroom in the battery to operate effectively.

I suppose Toyota could they have implemented a bifurcated charge mode (i.e., "Choose option 1 if you intend to operate as a pure EV after using Charge Mode, choose option 2 if you intend to operate as a hybrid.") and adjusted the final charge level accordingly, but that could just cause more confusion and/or problems down the road I suppose.

Again, this is all technically speculation (albeit what I'd like to think is educated speculation...)

No problem.

I was just pointing out there are also additional reasons why the traction batteries are normally kept within a charge range above minimum and below maximum.

 

[mejmea]

That is one reason but there are also several additional valid reasons.

Other than the first point, which is inherently built in, I would suggest that the others fall into the category of allowing for "optimal hybrid operation" - albeit DeepSeek was far more detailed (verbose?) than I!