Long Descents

If you only drive the car 4000 miles a year instead of 15000 miles a year the battery will be in better condition too. The car is intended to be used, some conditions will make it last longer than others. Driving through the mountains is probably harder on any car than driving on the flat lands. Will mountain driving make any difference in trade-in value in 5 years, not likely. Will driving 15000 miles/year rather than 4000 miles/year make a difference, absolutely yes. So don't worry about mountain driving, "just drive it".

 

Seems unlikely. If the numbers above are reasonably accurate, 3kWh charge in ~20 minutes, then we're a talking about ~9kW or 30-40A DC. Relative to the capacity of the battery that's a <2C charge rate, which is probably not particularly stressful.

FWIW ~30-40A average seems about right for sustained regen based on this data from a non-plug Gen3:
Downhill Regeneration Battery test! | PriusChat

Granted they are completely different batteries, but I would still assume that charging the PiPs battery at 2C is a lot less stressful than charging the liftback's NimH at 6C.

Rob

 

I often drive from 1800 feet to 6300 feet and back again. On the down, the battery goes from discharge to full in about 25 minutes, much faster than charging with the cable. After 34000 miles, I have not noticed any deterioration of the battery.

 

We need to start this discussion all over again!

1) We can drive the car every morning at 60 mph for 12 miles or a full discharge (85% to 20% SOC) in 12 minutes. Toyota does not suggest this would be a bad idea, they designed the car to do exactly that. While rapid discharge isn't as hard on the battery as rapid charge we can certainly do a full charge in 20 or 30 minutes on those occasions we find a hill/mountain road that would provide that rate/total regeneration.

2) The discussion about 1C, 2C or more C means absolutely nothing unless you know the configuration of the battery. "C" has to do with cells not whole batteries. If you have 10 cells in series a 2C charge rate (based on cell amp-hours) might be a good rate for actual full charge (near 0% SOC to near 100% SOC). For a 20% to 85% SOC a higher rate might be okay. If the 10 cells are in parallel the charge rate can be 20C for the same stress on the cells. The Prius battery is a battery not a single series of cells.

Conclusion: Whatever regeneration charging rate and duration the car computer will allow for whatever hill you go down at whatever speed is okay. The battery will probably still last 10 years or 150,000 miles.

 

Pargaraph 1 could be a matter of opinion since Toyota doesn't suggest it is or is not a problem. However, if you go uphill for the EV miles it becomes perhaps 6 miles and the discharge happens in 6 minutes. There is no suggestion in the manual that such should be avoided.

Paragraph 2 is science. A higher charge rate than 2C is clearly not a problem. If we know the structure of the Prius battery we can probably find out the 2C equivalent for the PiP. Source: any text book on electricity fundamentals. Think of it as maximum power for 10 resistors in series the same current runs through all 10 resistors, in parallel you need 10 times the current to run the same current through the 10 resistors.

Conclusion: I don't agree to disagree. I believe you are wrong.

 

As they say "You are entitled to your own opinions but not your own facts"

 

Substantially (10% 20% 30% ...) 200K miles and now your EV range is 10 miles instead of 12 miles. I guess its like insurance, you pay for it but you hope you don't have to use it. So if you wish to pay for very slightly lower mpg now in the hope that you will get slightly more EV range after 200K miles it won't cost you much. Meanwhile I'll enjoy that slightly higher mpg until I trade in the car at around 80K miles (8 to 10 years). Oh... and I don't have to worry about going down long hills, I can just drive it.

 

I go on mountain/hilly trips about once a month. I have never found a downhill where I could actually fully charge the battery in a continuous manner. I did find one recently where I got a full charge in about 45 minutes. However, the charging rate on the steep parts is the full 150 wH/minute for 4 or 5 minutes. By using regeneration as aggressively as possible my mpg for such trips is around 62 mpg whereas for long flatland trips I get around 52 mpg. I always use the recharged energy on the flat slow areas of the hilly trip for most miles.

 

Probably a safe bet that doing any driving mostly in EV mode for 200k miles will significantly reduce battery life. The question is if there is a significant difference between say:
1) using the EV capacity routinely around 60 mph (a typical commute for many)
vs.
2) routinely regenerating a large part or all of the EV capacity during long descents (many do this at least from time-to-time in CA).

I'm with most of the others here who have posted on the topic that don't seem to find robust data that there is a difference.

Toyota knew they would sell most and/or their highest percent of PiP's in California where mountains are plentiful and routinely driven on. Anything is possible, but knowing Toyota does not have a significant record of engineering snafus, it doesn't seem likely they missed this one.

 

That's a good point "mostly in EV mode for 200k miles will significantly reduce battery life". Clearly the number of charge/discharge cycles reduces battery capacity. My overall EV usage is around 58% which is A) why the PiP is great for my cost and mpg and B) clearly over shadows any degradation due to aggressive downhill charging. It does make me wonder about battery life for pure EVs.

 

FWIW my understanding is that the PiP pack is a simple 56s1p arrangement of 21.5Ah cells. The traditional calculation of charge/discharge rate is Current in Amps divided by Capacity in Ah, so 2C for the PiP pack would be 43A. The standard Prius NiMH pack is a 168s1p arrangement of 6.5Ah cells, so 6C is 39A.

From what I can find, there is very little data publicly available on the specific cells used in the PiP, so its impossible to gauge what the specific impact of charging at 2C might be. Based on what is typically available in the marketplace and the fact that Toyota used much better than average NimH cells in the standard Prius, I would be very surprised if regular charging at a 2C rate would have any significant impact on battery longevity. I would say that good tolerance of 3C charging is pretty typical, and again I would expect the cells selected by Toyota to be as good as or better than typical. Additionally my understanding is that high charge rate is primarily a concern near the extremes of SOC/DOD, where the PiP battery is already not allowed to operate.

Rob

 

Okay, I got it.
56 cells * 3.7 volts = 207.2 volts
207.2* 21.5 Ah = 4.4548 kWh
43A * 207.2 volts = 8.9096 kW (actually charging voltage is higher but ignore for simplicity)

4.4548 kWh / 8.9096 kW = 0.5 hours for a 100% charge
20% SOC to 85% SOC is a 65% charge
so we can charge in 0.325 hours = 19.5 minutes

The "Car Consumption" display shows a maximum of 150 Wh per minute
4.4548 kWh / 150 Wh = 29.7 minutes
so the maximum downhill charging takes 50% more time than the 2C rate hence not a strain on the battery and its difficult to actually find a hill that will charge at the maximum rate for 30 minutes.

 

The C-rate can apply to an entire pack assuming a pack with a specific capacity and a specific amount of power used for charging. If you talk about it in terms of energy/power, pack configuration doesn't matter.

Lets say you have 5 2V 1ah cells in series in a 10V/10Wh battery. If you charge at 1A/10V (10W) for 1 hour that's a 1C rate. If you have 5 2V 1ah cells in parallel in a 2V/1oWh battery and charge at 5A/2V (10W again) for an hour that's still a 1C rate even though the battery has a different configuration. Either way the c-rate is the same as long as the charging power and energy capacity remain the same.

http://web.mit.edu/evt/summary_battery_specifications.pdf