Here is a summary of the charge data from my UK Prius PHV, collected by my intelligent home charger, and exported to Excel. I've used a Pivot Table to see whether it shows much battery degradation, so I'm showing the max charge and number of charges per month, separated into years since the car was new. There is not really enough data for this year yet, year 4 (see below), but overall it looks fairly reassuring to me. I only charge at home, so these 525 charge occurrences include all of the charging for my vehicle. Current mileage is just under 21,000. The vast majority of my car usage is in EV mode, and we often go for months without needing to fill up with petrol. The car was purchased at he very end of March 2017, and so I've translated the years into financial years April to March. (That is the reason why there is no Jan - Mar for year 4 yet). Also note the following: 1. In year 4 (April 2020 onwards), due to lockdown and reduced car use, I've only charged the car from empty once, so the other figures for this year are incomplete charges. 2. The car is set to allow battery heating, so the winter figures may be a little higher due to power being used for battery heating whilst plugged in. 3. The total power use reported by my home charger is 2090.7 kwh. 4. Ideally I would have shown the months in financial year order, but it wasn't obvious to me how to do that and I decided that it is good enough as it is.
3% degradation? That’s about right. Although 3% of a Prime’s battery is smaller than 3% of an EV battery. But it’s also babied more than an EV.
Very nice! Thank you for sharing this data. Just one quick question and suggestion. Are the "max charge" shown in each cell for the month a single charge event or average of multiple charge events on that month? If it is just a single charge event highest in that given month, it may not be a real representative of your traction battery charge. The best way would be to average all of the full charges and only full charges (i.e. not including partial charges) under similar condition (such as same use of climate preconditioning or battery heater or cooler). And on your Grand Total cells, you just filled it with the highest charge in the given year. This again should be average of all 12 months. If you take the average of 12 data points, the number looks like this. That is 4.4% degradation of the max charge amount in Yr3 compared to Yr1.
The charger doesn't know which charges are from empty. So there is no easy of identifying those in order to find the average, unfortunately. That's why I did the analysis this way. It's the only possible way to get anything that might be meaningful, despite the limitations that you correctly identify. However, the only thing I know of that would cause incorrect figures, is the battery heater, and that only works in v cold weather. I don't think my car cools the battery while plugged in, in v hot weather? So if that's the case the summer figures may be fairly reliable.
Yeah, that's the problem. You have to log manually which one was from 0 EV range to full and which one was the partial charge. I did a similar data collection on my 2017 PRIME but did not log all of the charges to make the analyses complete. The graph below is the monthly average of all full charge kWh I have logged during my ownership of the 2017 PRIME for 30 months. I did not collect data almost the whole year from 5 mo to 17 mo making the downward trend incomplete. A single max charge could throw off the data trends. I had my 2020 PRIME since March. I have not been driving much, thus I have only done small numbers of full charges, but the highest charge I had was 7.13kWh for a full charge for unknown reasons. This is an outlier of the data I would not want to include in the analysis. Also for cooling the battery, it is true that the battery cooler function cools down the battery using climate control BEFORE the charging event starts, however, I have learned recently that even during charging, the battery cooling fans run to cool the battery. If the temperature inside of the car is hot, the fan seems to run harder. I noticed my day time charge for an empty to full took ~0.2kWh more to finish charge than a night-time charge.
Ok, thanks. I did do a bit of data cleaning, and removed a very few days points that seemed unreasonably high. Should perhaps have said that. These were 8.1, 7 and suchlike. But the reason for including data by month was to help identity months where battery conditioning might have taken place. Mind you, even what is empty is variable in any case, depending on the state of the hybrid portion of the battery. We have a downhill section when coming home, where the battery gets a regen top-up, so this must reduce the degree of emptiness, even when the ICE is running because EV mode was exhausted.
Yap, that will throw in another variable. The big one that is. You might be interested in reading @PiPLosAngeles analysis in this thread. He is trying to eliminate this variable of HV depleting (or regen adding ) 0% EV SoC on the display. From his somewhat small numbers of data points, he found that, in his 2017 PRIME, there has been no battery degradation in 3 years from the full charge amount he is reading for strictly from 0% to 100%. What is your miles/kWh (total average electricity consumption) on the "Drive Monitor 2" | Page 12 | PriusChat
My approach has been to film the same drive under the same conditions year after year. I just did the capture this morning for year 3. EV distance was a little over 30 miles... matching the previous drives. That means based on observations so far, you get the experience of consistency. There is the possibility of a degradation buffer, extra capacity only accessed as the system detects reduction. Whatever the case, that is still a result in excess of the EPA rating. Crude evidence of this is the calculation from my own charging. 6.0 kWh has been the max I typically can squeeze in, without conditioning. 72% capacity is max for observed EV delivered via plugging in. That doesn't account for losses from the charging process or gains from regeneration though, which a rough guess would be 10%. That would equate to a true 5.4 kWh for EV usage per recharge... which is quite a bit less than one would expect from a 8.79 kWh capacity battery-pack. Others reporting more kWh per charge may have a combination of less efficient charging and the possibility of different tolerances in the software for their vehicle. Long story short, we may never find out. Knowledge, like long-term strategy, is too valuable to disclose. They need a competitive edge.
Remember, as has been covered elsewhere in this forum by people like Lee Jay and others, that the 8.79 kwh battery is partitioned in the following ways: 1. Top (unused) reserve for battery longevity 2. EV use portion 3. Hybrid use portion 4. Bottom (unused) reserve for battery longevity So, that is why the usable EV portion is much less than total capacity. I like your idea of making the same drive and comparing those, year by year. Maybe your weather is more consistent than in the UK, but obviously weather and associated HVAC use are additional variables in that scenario.
That doesn't actually add up to 8.79 kWh though. Based on the basic tools we have for measuring draw & consumption, there appears to be a small amount missing. True, it could be some other property of rechargeable batteries we are not aware of. But then again, we already know about the difficulty of measuring conversion, vampire and storage losses. We aren't the only ones making that same observation/speculation about automaker approach either.
