battery capacity (estimated range) decreased by 30%

yes, completely. unfortunately, 25 miles is only an estimate based on epa controlled testing. as you said, winter vs summer is expected.
and of course, there are many other factors involved. heat usage, tire pressure, driving style and etc.
how did it do during the winter of 20/21?

 

If you bought the car in March 2020, then this is the second winner. How did the car operate last winter? If it did better than this winter, then is this winter particularly colder than last winter? Unfortunately, in a colder climate, losing up to ~50% of the EV range in the wintertime is perfectly normal. I bought my 2021 PP last July and it has only 4K miles on it. I was getting an average of ~35miles of EV range (42miles was my top EV range on the record) before it got cold. Now it is cold, I am lucky if I can get a 20miles of EV range on colder days.

This is my third Prius Prime (2017, 2020, and now 2021). All of them behaved similarly in colder months. You really can't avoid this loss of EV range during winter.

 

Mine is now showing ~25miles (with HVAC) or ~29miles (without HVAC), but the EV range shown on the GOM is meaningless. I can make it show near 50 miles if I manipulate the EV/HV driving by switching. Likewise, if I am very careless or my wife drives the car for a few days, it will show ~20 miles or lower in very short order.

What is your monthly average miles/kWh shown on the Eco diary? If it shows a very rapid drop like mine, then it is not a surprise that your EV range on the GOM drops very quickly.

 

forget the guess o meter, if you were able to make your commute last winter, and nothing else has changed, you need to look at other things besides the battery.
the reason i say that is that nothing can be done about the battery, but if it is something else, like a dragging brake, it can be rectified.

 

Thanks for the update. It will be very interesting to see what they will find out about the battery capacity. When you do take it for the test, make sure you get a hard copy of the result of the battery analysis. I have not seen one. It would be very informative what Toyota's diagnosis shows on the battery capacity test like this.

BTW, your statement below indicates that the problem is not the battery capacity. The monthly miles/kWh reduction seen in Oct-Dec is perfectly in agreement with what you are seeing on the GOM. At the number, you are recording, which is below 3 miles/kWh, it would be very hard to get anything above 20 miles of EV range either on GOM or in real life. Remember that you have less than 6kWh of usable traction battery capacity for EV mode when the battery is full. 2.2miles/kWh x 6kWh = 13.2miles. So, at this efficiency, you are not going too far even if you have a healthy full capacity traction battery. The EPA number of 25miles of EV range corresponds to 4.1 miles/kWh (assuming 6kWh of usable battery energy on EV mode). So, if your monthly or daily average on the Eco diary is showing less than 4miles/kWh, then Toyota is likely to say your driving is causing the low efficiency, not the capacity of the battery. If it was the battery capacity issue, then your monthly average should stay the same yet you see the total EV range diminishes.

Just for a reference point, I have never gotten my monthly average EV efficiency to go below 3miles/kWh on my PPs. For my current 2021 PP, the overall average is currently sitting at 5.1miles/kWh with a range of 4.0 to 5.6 for the last 6 months. (4.0miles/kWh is for Dec average).

For my 2017 PP, the graph below was the plot of my monthly EV efficiency number. The lowest points were 3.1miles/kWh seen in the second winter, Dec and Jan (the first month on the graph is July). One data point showing 0.0miles/kWh is when I did an entire month without charging the car. Thus everything was HV mode and no EV efficiency was recorded. Naturally, the dip in the average happens in the winter months when it's cold. My third-year average was much better than the first two because I experimented with artificially increasing the miles/KWh value by switching EV/HV. But the overall real EV range was not changed much. That is I get 30-33miles in warmer months (5.0-5.5miles/kWh x 6kWh) and 18-21miles in the coldest winter months (3.0-3.5miles/kWh x 6kWh) and somewhere in between in shoulder seasons.

 

try setting the temp to 'low' and fan off.

ask the dealer what that will cost. if it isn't covered by warranty, (and it isn't) you will have to pay.

any change in tires or pressure?