Extended charge all the time?

I know this is in the manual but couldn't find anything here.

I am guessing that using extended charge all the time will degrade the battery faster.

Are you all just using it every now and then when you know you will need more charge? Or only using it with scheduled charging to the EV doesn't sit as a high SOC for long before you are out the door in the morning?

As recommended by Toyota (Tesla?) I only do "extended" charges rather sparingly; on average maybe once or twice per month. In most cases the range of the RAV4 EV is more than adequate (~100 miles) after only standard mode charging. It is just not necessary to do extended charging for any typical around town driving and/or for daily short mileage commutes.

One school of thought says it does not hurt to recharge every day or mulitple times per day, and another suggests the battery will live longer (decades pershaps?) if the SoC is kept as close to 50% as much as possible. This can lead to OCD quite quickly, so my recharging is only about once per week, and then only in the standard charging mode. However, I usually do not wait till the "turtle mode" to recharge - far from it - so I am probably more biased toward the 50% rule.

Scheduled charging is really not very reliable in these cars, at least (still) not yet, so I generally recharge on Saturday or Sundays, when PG&E has the most flexible "TOU" lower rates.

We have one member here "kohler" who is doing some experimental stress testing of the same Li-ion cells used in the RAV4 EV battery pack (Panasonic 18650A). We are all anxious to find out the results of his testing, but suffice to say, these cells, like all other Li-ion batteries, do NOT like heat. The more often and longer you recharge them, (as in the optional extended mode), the longer they are exposed to elevated temperature. Just be glad Toyota (Tesla?) had the good sense to put in a battery pack thermal management system with liquid cooling (and heating) to keep the pack as close to optimum operating (and storage) temperatures as possible. I believe charging even at 10kW limits the charging to a relatively low rate, which helps to prevent overheating.

If you do charge to 100%, please don't let it sit long, particularly in hot ambient temperatures.

Dsinned said:

The more often and longer you recharge them, (as in the optional extended mode), the longer they are exposed to elevated temperature.

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I think Dsinned meant to say they would be exposed to elevated voltage, not temperature. The charge rate is so slow, no heating will occur because of charging.

I believe using the extended mode charges the cells up to 4.15V and holds them there for approximately 35 minutes vs ~4.05V (and instantly shutting off) for standard mode. The longer the electrolyte is exposed to higher voltage, the more chance it has to break down over time. My testing should show how much degradation occurs between charging to the two different voltages.

I think the extended mode charges the cells up to 96% while the standard charges them to 83% state of charge (of true capacity).

My mistake, I think you're right about the cell voltage under charge . . .

But, 96% of true capacity for an extended charge, I think is too high. Solving for "x", 0.96 * "x" = 41.8kW, therefore, "x" = 41.8 / 0.96 = 43.54kW. That does not seem right. I think the true capacity of our RAV4 EV battery pack is about 47.79kW conservatively speaking, based on the no. of cells (~4500), nominal cell voltage of 3.6Vdc and individual cell capacity of 2950mA-hr. Thus, the upper SoC percentage after an extended charge would be equal to 41.8kW / 47.8kW, or ~87%.

Using the same proportional relationship for a standard charge, 35kW / 47.8kW = ~73%.

So, there is about a 15% differential between SoC to true capacity, comparing a standard charge vs. an extended charge.

However, we know that the lowest SoC can't be zero, so these percentage have to be adjusted upward, or same for the true capacity (perhaps closer to 50kW), so maybe your percentages are actually more accurate.

I wish I was better at math, but does this seem logical?

The LEAF cell are charged to 95% SOC and discharge to 2%.

My wife does a great job of keeping our Volt from using any gas on her commute. Considering that has about 1/3 the range of the RAV4 even in normal mode it would be nice if we could keep even a tighter SOC setup with the RAV4. We want to keep this car as long as possible, so battery longevity is a big deal for us... A 40-70% SOC window would even work for us most of the time.

Dsinned said:

But, 96% of true capacity for an extended charge, I think is too high. Solving for "x", 0.96 * "x" = 41.8kW, therefore, "x" = 41.8 / 0.96 = 43.54kW. That does not seem right. I think the true capacity of our RAV4 EV battery pack is about 47.79kW conservatively speaking, based on the no. of cells (~4500), nominal cell voltage of 3.6Vdc and individual cell capacity of 2950mA-hr. Thus, the upper SoC percentage after an extended charge would be equal to 41.8kW / 47.8kW, or ~87%.

Using the same proportional relationship for a standard charge, 35kW / 47.8kW = ~73%.

So, there is about a 15% differential between SoC to true capacity, comparing a standard charge vs. an extended charge.

However, we know that the lowest SoC can't be zero, so these percentage have to be adjusted upward, or same for the true capacity (perhaps closer to 50kW), so maybe your percentages are actually more accurate.

I wish I was better at math, but does this seem logical?

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Yes, we have to account for the unusable capacity at the bottom end, which I estimate to be 0-8% SOC.
So I think true capacity is ~47kWh (100% SOC), extended charge setting charges up to 45kWh (96% SOC), can't discharge below 3.75kWh (8% SOC), leaving ~41kWh usable in between. For standard charge, which charges up to 39kWh, that leaves 35kWh usable.

Kohler Controller said:

Yes, we have to account for the unusable capacity at the bottom end, which I estimate to be 0-8% SOC.
So I think true capacity is ~47kWh (100% SOC), extended charge setting charges up to 45kWh (96% SOC), can't discharge below 3.75kWh (8% SOC), leaving ~41kWh usable in between. For standard charge, which charges up to 39kWh, that leaves 35kWh usable.

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The published 100% charge of 41.8kWh usable seems very accurate, as does the 80% charge at 33.44kWh usable.

What that actually translates in SOC%, as well as a lot of the other data, is waiting for us in the EV-CAN buss.

Tony, the most often "published" standard charge in terms of USEABLE capacity is "35kW". In all of Toyota's references to this, I don't think I have ever seen any other value given. I do concur that "41.8kW" is the published value for an extended charge. What these translate to in terms of SoC is pretty much still anybody's guess, but "Kohler Controllers" seems to be on the right track.

New development. After characterizing the Panasonic NCR18650A 3.1ah cell, I'm not sure they are the ones in our RAV4EVs. Their internal resistance is just too high for general EV type loads. I'm also testing a different cell which has been suggested to be the one used in the Model S and possibly our RAV4EVs, the Panasonic NCR18650PD 2.9Ah cell. Although Panasonic makes several cells using their "NNP" technology, 2.9Ah, 3.1Ah ("A"), and 3.4Ah ("B"), these are all designed for low rate applications, like laptops. However, this new "PD" series has lower impedance (1/3 less) and can handle continuous currents of 3.5C and bursts of 5C. This proves true when going through the DST profile simulating loads from our vehicle's driving. The average voltage is much higher throughout the discharge and the min and max voltage is much tighter. The voltage drop of the "A" cell is just too high at lower SOCs.

Under this scenario, 4494 cells would still give ~47kWh, Extended Charging would charge to 95% (or 44.6kWh) and standard charge would charge to ~81% (38kWh). Assuming we are leaving 6% at the bottom to protect the system (2.82kWh), that still leaves 41.8kWh and 35kWh usable respectively.

I will continue to test both cells, but my money is on the PD series.

I know this is VERY difficult to find out without any "IP" disclosures from Toyota or Tesla, so you have to draw the line somewhere on your assumptions. If only somebody here knew of a "wrecked" RAV4 EV that could be visited to look inside the battery pack, but even then it might not be possible to see any of the actual cells. Do you know if the "PD" type cell has been available from Panasonic from about at least a year ago? If not, how could they be used in our cars, which must have started their production lifecycle at least 9 monhts ago.

I have a casual friend that works in the Fremont Tesla factory I will probably see this Sunday at a social event. If so, I will ask her if she can find out and let us know. No promises though - I wouldn't ask her to do anything that could jeopardize her job at Tesla.

Dsinned said:

Tony, the most often "published" standard charge in terms of USEABLE capacity is "35kW". In all of Toyota's references to this, I don't think I have ever seen any other value given. I do concur that "41.8kW" is the published value for an extended charge. What these translate to in terms of SoC is pretty much still anybody's guess, but "Kohler Controllers" seems to be on the right track.

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Yes, I know they say 35; my numerous drives suggest 33.44kWh, or 80%... Just like a LEAF.

EPA even gives the Rav4 and LEAF a special notch, with a 80% and 100% range data averaged. The only two EVs with that honor.