2021 Plug-In Battery Question

As the manual indicates, it is recommended to do this to prevent battery capacity reduction. Switching to HV before storing ensures that the battery has a low level of charge in the traction battery before storing the car for a long period of time. Many are contending that this practice is not the best practice, and the battery should have some (ideally 30-40% SOC) left in the pack.

I personally found that it did not really matter much at least for the first year of use and leaving full charge for a few days occasionally. My take is that unless you intend to store the car for months at a time, the recommendation probably does not apply to the car being driven regularly meaning at least a few times every week.

 

I am not questioning the need to store in a low SOC. Rather….

But we can have a low and optimum SOC without selecting HV mode. Inversely, I can have a high SOC prior to selecting the HV mode and after the selection of HV mode depending how long I drive for.
Selecting HV mode dies not ensure optimum SOC.

Why did the manual not simply state that to deplete the SOC to less than 8 miles prior to extended storage of X days or more?

The manual states to switch to HV mode prior to powering down independent of SOC. Why?

iPhone ?

 

I think the intended message is to let the EV range depletes and switches to HV mode "automatically". I don't think it is suggesting the operator manually switches to HV mode when there is still an EV range left (meaning SOC is not empty).

 

Do those apps show 40% to 80% for NiMH models? Are the cars dwelling at 100% for extended periods, or do they make use of that energy right away?

A true 100% SOC for extended periods sounds like a bad practice for a device that is used outside of a climate controlled environment.

Thinking about it, the 90% charge range on the app can't be right. It is a 8.8kWh battery with a usable capacity of around 6.7kWh. That's a 76% SOC range. The app is likely just reporting the same data going to the dash display.

If that is really what it took to have a hybrid battery last the life of a car, there'd be less reports of how long this things can actually last. Most drivers aren't going to do that. toyota never recommended it, and the US market didn't even get an EV button until the midcycle of the gen2 to make it possible.

The gen4 also isn't the first Toyota no-plug hybrid to use Li-ion. The Prius v/+/Alpha had variants equipped with Li-ion.

The OP's question wasn't about storing the car though. They were asking about best practice while the car is in use. Do you turn on hybrid mode when the SOC reaches that 30% to 40%? Do you circle the block if the SOC is higher than that when you reach your destination?

No, because you are using the car. Not parking it for a week or more. There are many variables that effect a battery's health. Some are in conflict with others. Deeper depth of discharge leads to shorter life. Reducing that wear entails keeping the battery as fully charged as possible. Keeping track of all these parameters would be a burden on the user. The buffer in the battery and BMS is there to do the job of ensuring the battery's life.

The owner's manual has important info for the user. It also contains statements to protect the manufacturer.

The 40% limit is recommended for storing any Li-ion battery to account for self discharge. Store a battery at too low a charge, and it takes less time for the self-discharge to drop it into a damage risk zone, or even cause the battery to brick.

Toyota doesn't define storage, because they can't account for all the possible conditions the car will be stored in. Keeping the battery at 100% in a cold climate is less risky than in a hot one for instance. I'd go by concern for the 12V. If the car is going to be parked long enough that it could go flat, then I'd follow the storage recommendations in the manual.

The battery isn't the only thing to address when storing the car. For those that mostly drive on EV, switching to HV before storage ensures all the metal surfaces have a coating of oil, and fresher gas is in the fuel lines.

 

Good point. Thanks.


iPhone ?

 

Good point about oil distribution before storage.


iPhone ?

 

Strongly disagreed here. On the contrary, having a cold internal-combustion engine kick in for a few seconds before you turn it off and store for an extended period of time is detrimental to it, with all the fuel and hydrocarbons coming from cold combustion mixing with the oil before you store it, not to mention depleting the protective film layers during cold-engine running, which has the highest engine wear, and not giving a chance to replenish those film layers.

If you are going to store the car for extended periods of time, you need to drive the car in the HV mode for at least fifteen miles before you turn it off. This will ensure that the additive film layers on the metal parts will be fully reactivated (heat is necessary for reactivation) and the harmful contaminants in the oil will evaporate. Long trips are good for the ICE; short trips are bad, and on–off of a cold engine is detrimental.

 

Exactly. It just shows how incompetent those Toyota engineers who write owners manuals are. Owners manuals used to make sense in the past and had a logical basis—they no longer do. One of my job job duties is to write technical manuals, and I can't stand poorly written technical manuals.

 

It isn't my suggestion.
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Toyota is the one telling owners to shut an unwarmed engine off in an effort to protect the battery during storage.

 

That has nothing to do with oil. Toyota wants to ensure that the lithium-ion battery is not in a charged state during storage. Many owners have no idea where they can see the battery percentage, and this is a simple way of Toyota having owners ensuring that the battery is discharged before storage.

 

The gases from the ICE also contain low concentrations of corrosive compounds, which then condense in a cold exhaust system. Over time this corrodes the metal parts of the exhaust such as the muffler and exhaust pipe, which then need servicing and replacing. This is not a great problem if the engine is always run long enough to heat the entire exhaust system but frequently turning the ICE on for a short period will accelerate corrosion of the exhaust system.

 

But it results in the negatives you brought up about storing with an engine shutdown cold.

 

Toyota is not as much worried about that as the battery. Remember that they have a much longer warranty on the EV battery (10 years, 150,000 miles) than on the internal-combustion engine (5 years, 60,000 miles). Moreover, they don't really mention a cold engine.

 

Agreed. Also, the gases from the ICE also contain low concentrations of very corrosive compounds, which then condense in a cold exhaust system. Over time this corrodes the metal parts of the exhaust such as the muffler and exhaust pipe, which then need servicing and replacing costing $$. This is not a great problem if the engine is always run long enough to heat the entire exhaust system, however, frequently turning the ICE on for a short period when cold will accelerate corrosion of the exhaust system. Gokhan is right - run the ICE until warm.

Which then begs the question: when driving in EV mode at around 100 km/h (= 60 mph) the ICE cuts in automatically for a brief period even for a little acceleration. The ICE then stays on for a few minutes (presumably to warm the engine a little) before automatically shutting down. So, these short periods of use on frequent occasions are presumably also less than optimal? (Our Toyota Prius PHEV - Japanese import - doesn't have EV-City mode.) My daily commute includes 10 minutes of highway driving covering most of the journey so I would really prefer to be 100% EV and charge overnight (at 6 Amps). Any suggestions about how to prevent the ICE cutting in for such short periods without EV-city mode?

 

Those corrosive compounds are mostly water. The warm up cycle when the engine first comes on is to warm up the catalytic converter, so the exhaust system likely is also warm. That doesn't address the water that got into the oil, which then forms acids.

Aside from being easy on the accelerator, there probably isn't much that can be done to keep the engine off with a PHV. It might be possible to 'tune' the modes to North America Prime specs. You'd lose EV City and get our EV mode, which nearly always stays in EV up to 82mph. Your EV mode is what called EV Auto here. It could be more burdensome than making selections in the software, like a NA ECU transplant.

There could be other options, but most of Priuschat's user base are driving Primes.

 

Agreed, the exhaust gases are mostly water and only dilute acid.

If I could even just minimise the ICE cutting in up to 110 km/h (70mph) then I'd be happy. Since our PHV doesn't have EV-city then tuning to some of the North America Prime specs might just do the trick. How could this be done? Could I do this, perhaps using an OBD2 connection?

 

What modes do you have? I only know of North America(EV, EV Auto, and HV) and Europe(EV, EC City, and HV).

 

The biggest contaminant will be fuel dilution because a cold engine cannot burn the fuel fully. That fuel wil oxidize the oil, which may harm the engine

A cold engine cannot fully burn the air–fuel mixture, and there is a lot of fuel dilution of oil resulting, in addition to water vapor and partially burned hydrocarbons mixing with oil. These contaminants won't go away and may degrade the oil and cause harm unless the vehicle is driven for over ten miles.

In addition, a cold engine cannot reactivate the antiwear/extreme pressure/friction modifier film layer on the wear surfaces.

 

The harm with fuel dilution of the oil is in the dilution. It thins the oil, lowering the viscosity, and reducing lubricity. It is more of a concern with diesels, as that fuel doesn't quickly boil off. Not long ago, Mazda diesels had an issue in which the volume in the crank case was increasing from the fuel getting into the oil.

Most of the oil oxidation is due to the heat of operation. In time, it leads to sludge formation. Over the maintenance interval, the oil viscosity will just increase some. Water in the oil will react with the oxidized compounds though. When it does, acids are formed.

For every molecule of octane burned, 9 of water is produced in the cylinder. Mass wise the water out weights the octane by 1.42. About a third of the fuel would have to not burn for it to be more than the water in the exhaust mix. Then the water blow by doesn't end when the engine is warmed up.

 

You are obviously not an oil expert, so you did a lot of Google'ing to look this up, but that's not usually how the acids in the oil form. Moreover, fuel dilution is not limited to diesel engines. It is very common in gasoline direct-injection engines, where it can be severe. It will also happen in any engine that does frequent short trips because a cold air–fuel mixture does not burn completely. Of course, fuel dilution will reduce the oil viscosity.

Acids are formed by oxidation, nitration, and sulfation of the oil. Regarding oxidation, ASTM D7414 best describes it:

A large number of compounds, such as aldehydes, ketones, esters, and carboxylic acids, are produced when oils react with atmospheric oxygen. Oxidation is measured using a common FT-IR spectral feature between 1800 cm–1 and 1670 cm–1 caused by the absorption of the carbonyl group present in most oxidation compounds. These oxidation products may lead to increased viscosity (causing oil thickening problems), acidity (causing acidic corrosion), and formation of sludge and varnish (leading to filter plugging, fouling of critical oil clearances and valve friction).

Sulfation occurs when sulfur in the oil or fuel turns into sulfuric acid.

Nitration occurs when NOx from combustion mixing with oil turns into nitric acid.

Other contaminants like fuel, partially burnt fuel, and blowby will also oxidize the oil.

Detergent bases in the oil (calcium- and these days both calcium- and magnesium-based for LSPI protection) will help neutralize the acids to some extent until they are depleted (the total base number TBN becomes very small) by the acids formed by oxidation, nitration, and sulfation of the oil (until the total acid number TAN well exceeds the TBN).