Calling a spade a spade

Although Toyota recommends keeping the battery at 11% SoC (EV to HV auto transition) for longterm storage; perhaps to keep it simple for the general public.

 

this is exactly the point of the charge schedule. And in addition to this and if I remember this correctly from training which was 2016! These batteries are least stable at higher SOC and very low SOC. Not 100% or 0% I mean within the allowed range. So leaving that battery say for a couple of weeks at max allowed SOC is not the best for it. But at the same time doing that every night for say 6-8 hours X time in years has the same negative effect.

Off topic but I have to say this. if you are on this forum you know a lot more than the average prime owner A LOT to a point that you’re not even on the same planet! We still have to answer some pretty interesting question to new car owners that makes me wonder always Are you sure this is a good idea? I actually recently had an interaction with a customer with a Prius prime. Very nice older gentleman in for a 10k service and also wanted a aux battery test. Of course the lube tech is fumbling in the hatch area trying to find the battery which is conveniently staring him in the face when he opened the hood but force of habit from the 3rd gen. I walked by and I had a feeling that a lube tech had no business fumbling with a $10k battery so I asked what he was up to and there I see the included charging cable with the prime in a plastic bag! Yes basically never opened! I talked to the gentleman and his replay was he liked the look of this one better than the “base model” Prius. So here’s a prime owner who has never used their EV range in 10k miles! It happens and I blame that one on sales. Customer was happy in the end to find out that the prime came with one more option and possibly the best one! The EV range. A car dealership is an interesting place to work in! Let’s leave it at that.

 

OK, your statement on the very low SOC being bad for the battery is contradicting what Toyota suggests in the manual. To prevent degradation of the traction battery, Toyota suggests keeping the traction battery SoC at 0% on the dash which is roughly equal to 8%-14% real SoC while leaving the vehicle undriven for a long period of time whatever the length that might means. As I stated in my previous comment, taking from various readings in this forum, I have been keeping my car's traction battery at 30%-40% SoC on the dash which is roughly equal to 35%-45% real SoC rather than at 0% while the car is parked prolonged time at the current COVID-19 restriction. What is your take on this?

 

How to Prolong Lithium-based Batteries - Battery University

 

And per this: BU-1003a: Battery Aging in an Electric Vehicle (EV) – Battery University
"Li-ion must be shipped at 30% SoC; the recommended long-term storage is between 40–50%."

"The combination of low cycle-depth and low SoC leads to the longest battery life, but this does not fully utilize a large, heavy and expensive pack. To avoid resistance increase through deep a discharge, the onboard BMS always keeps some reserve capacity while indicating “empty” wrongly. Reserve capacity also protects the battery when charging at a high current because a completely discharged Li-ion cannot tolerate an ultrafast charge. For best results, charge more often without going full charge."

"
Simple Guidelines to prolonging the EV battery

• Limit ultra-fast charging, especially when the battery is cold. Use Level 2 when possible.
• Only charge the battery to the level needed for the daily routine. Full charge hastens capacity fade.
• Charging to 100% is filling to grace capacity. The grace capacity is not disclosed, however, Japan requires displaying the actual capacity on new EVs for vehicle resale value.
• Do not discharge the battery too low as this increases the internal resistance. Charge more often.
• Charge and use the battery at room temperature. Operating when cold reduces capacity.
• Store the battery in a cool place at partial charge. Usage and storage have different requirements.
• Moderate the battery to room temperature in winter before charging and driving. The BMS may do this automatically.
• Charge the EV after a sabbatical. Resting at low charge reverses capacity fade.
• It is best to let the battery rest at low SoC and only charge before use. Dwelling at low charge reduces calendar aging and may also reverse capacity fade."

The last 2 bullet points are interesting. Also, perhaps Toyota uses a different Li-Ion chemistry than the ones covered in the article, so prefers a lower SoC for storage?

 

Also, I am curious: are dealers advised by Toyota to leave the Primes at 0% (allowed) SoC (the transition SoC from EV to HV) so battery doesn't degrade? I came close to purchasing a Prime last month, that was with the dealer since June 2019. The sales person mentioned to me their service department regularly charges them (whatever he meant by "charging"). Do the service departments know to maintain the Primes on the lot at low SoC?

 

That is a misunderstanding of what "low" actually represents. Basically, it means a "not charged yet" state. In other words, Toyota recommends leaving the recharge until right before the vehicle is to be used.

Allowing the chemicals to rest as long as possible before routine charging is as a "cold soak". This does indeed help slow aging.

In simple terms, you are giving time for the battery to cool down. Heat is what reduces longevity. That is why DC fast-charging has so much more of an impact than just level-2.

 

Yeah, but the Toyota's wording in this case is very specific. "After confirming that EV mode has switched to HV mode, turn the power
switch off." That is --% (= 0%) SoC on the dash display or 8%-14% real SoC in the traction battery, not an arbitrarily SoC that is a "not charged yet".

 

What case is that specifically, long term?

My reference (also from Toyota, a video quote from the PHV reveal) is for overnight.

 

I have heard on this forum that Level1 consumes more energy than Level2 for the same charge put into the battery. Does it mean Level2 is better than Level1 for battery longevity?

 

The time for "a long period of time" is not defined in the manual. But taking it literally, it basically means what @Gokhan said.

I don't know the chemistry of the battery or physics of battery degradation, but it is interesting that different source posted by @srivenkat recommends to do this to prolong the life of the traction battery.

Again, currently, I am keeping my Prime at 30%-40% SoC most of the time with minimal drives, but this goes against the above suggestions. I really don't know if I should let the car sit at 0% SoC or 30%-40% SoC.

 

It should be other-way around. In theory, L1 being slower and lower Amp will generate less heat, thus better for the battery longevity than using L2. But for most part in real world practice, I don't think there are much differences.

 

F

Is this true considering the heat generation with the excess energy with L1 that I have heard about in this forum?

 

Also, for clarity in these discussions, could we standardize on SoC % references on the real SoC % as we would see on HybridAssistant?

 

We have found documents stating the difference exists but is negligible. Other factors, like heat from the sun while parked, has a far greater impact.

 

I don't know if anyone has measured heat generated on the traction battery during L1 vs L2 charging. Yeah, 120v 12A L1 may produce more heat on EVSE brick being less efficient than at 240V 16A L2 EVSE, but does it produce more heat on the battery?

Then only ref I know about the comparison of different charger used is in this source. What can 6,000 electric vehicles tell us about EV battery health? | Geotab
Toward the bottom of the page, under subtitle "Taking a look at charge type" the article states following.

While Level 2 is often cited as the optimal way to charge an EV, the difference in battery health between cars that routinely charged on Level 2 as compared to those who used Level 1 appeared to be observable but was not beyond the level of statistical significance.​

So, I guess, although statistically not significant, L2 is better for the logevity of the battery as you say, but is it because of the heat? The article doesn't speculate why.

You can try, but not everyone know or use HA.

 

The extra energy consumed by Level 1 may not be, and likely aren't, in battery. It can be losses in the charger and EVSE that add up over time.

While Level 1 may generate less heat in the battery than Level 2, the battery sits at higher temps for longer. This is where effectiveness of the cooling system comes into play. take the heat away quickly enough, and there could be no difference between the two in terms of battery life.

 

I agree john I think this is the primary reason for their recommendation. The RAV4 prime which is essentially an evolution of the Prius prime uses the A/C refrigerant to cool down the battery and still has a heater for the battery not exactly similar to the Prius prime but close.

The other one that we had a small debate at training which didn’t make sense and we couldn’t get an answer from engineering is somewhere in the owners manual it says to charge the battery in a well ventilated area and it even specifies not a closed garage. That was a prototype manual we were debating on that language could have changed anyone notice that? I haven’t really looked and don’t really want to include it in a video recommendation as people might get infuriated and shoot the messenger.

 

I remember reading this language with regard to Charge-mode for sure, understandably because they didn't want people to use Charge-mode (which uses the engine to charge the traction battery; for newbies that might chance upon this post) in a closed garage. I haven't studied the manual in its entirety, so it's possible someone whose English isn't strong may have copy-pasted this same language elsewhere in the manual.

This is significant, the lack of which, kept me away from considering the Prime for a long time, until I succumbed to its other charms. Either the RAV4 is harder on the batteries, or the price-point made it worthwhile to add liquid-cooling or Toyota has woken up to the importance of liquid cooling and we will see it in the next Prius Prime generation as well.

[Emphasis in above mine] Thanks for the detailed explanation, AMD. Looks like there's some provision for sediment, any phase separated ethanol/water, etc., from getting sucked in, because of the pump being on the side slightly above the lowest point.

 

The Escape and Explorer hybrids have liquid cooling. It allows a more compact battery pack. That was probably a big reason for why the Rav4 has it. Air cooling would mean a bigger pack with more interior space loss.

Calling refrigerant based cooling liquid is misleading. It is only a liquid under pressure, and is a gas in the cooling loop for the pack. that is a technical quibble, but it leads to operating and design differences. Liquid at atmosphere, mostly water, systems can also heat the pack with the simple addition of a heater to the coolant. The refrigerant cooling needs a separate heating system, or a major redesign to have heat pump operation in the pack.