New ‘23 Prime - tracking MPG and energy?

Congrats on your new 23 Prime. You must be one lucky person to find one available to buy. I have not seen the new Gen5 Prime (MY 2023 Prius Prime). My comment is based on the Gen4 Prius Prime (MY 2017-2022). If Toyota has not changed how they display the efficiency (MPG and miles/kWh), there is no easy way to monitor and record the HV portion of the gas mileage (MPG) or separately measure the amount of charge used for the EV operation. If you charge the traction battery from the wall and drive a PHEV with battery power EV mode, then your MPG will include the EV distance in the MPG calculation.

If your main objective is to record and analyze the cost efficiency of the car, then the only way to semi-accurately keep a record of the both EV and HV portion of the cost is to measure the kWh used from the wall to charge the traction battery. I have used a "kill-a-watt" meter for my L1 EVSE for this purpose. If you use L2 EVSE, there are many that come with a WiFi app that monitors energy use during a charge session or installs a 240v watt meter on your L2 EVSE line.

Toyota App has information on the charging and may display the kWh value, but from what I have read in other threads, it is extremely inaccurate (underestimate 30-50% of real kWh used at the wall). This seems to be somewhat common in many PHEV apps by various manufacturers. I currently drive Ford Escape PHEV. Its app reports the kWh used for each charge session, but the value is always lower than the actual kWh indicated by the "kill-a-watt" meter.

BTW, if you just want to know EV vs HV which is cheaper, then you can just use the EPA-rated EV range and gas mileage. For my (MY 2017-2022) PPs, it was almost always cheaper to drive on gas using HV but the difference was not big. This is because I live in a region with a very high electric rate and relatively cheap gas. The only time EV mode saved money was when gas prices soared to above $5/gal in early 22.

Here is the part of the spreadsheet I kept for 21 PP. I am keeping the same type of record for my current PHEV.

 

For your 2023 Prius Prime XSE, assuming the EV range of 39 mi and gas mileage of 52mpg, and it takes ~11kWh to fully charge the traction battery.

The cost of operation is

• eclectic rate ($/kWh) x 11 (kWh) ÷ 39 (mi) = $ cost per mile EV
• gas price ($/gallon) ÷ 52 (miles/gallon) = $ cost per mile HV

For my area, with the local electric rate of $0.34/kWh and the gas price of $3.40/gal. HV is substantially cheaper now.

• For EV $0.096/mile = $0.34($/kWh)x11(kWh)÷39(mi)
• For HV $0.065/mile = $3.40 ($/gallon)÷52(MPG)

 

As @Salamander_King described, I also used a spreadsheet to track electricity and gas use and then convert that to cost per mile. And cost is the bottom line.

 

I wouldn't be overly concerned about daily tracking electricity and fuel cost in your Prime. In my case, electricity is 13 cents per KWh and I once figured it cost about 80 cents to charge my car to get an average of 25 miles. With gas it gets about 50 mpg, so in either case it is an economical car. The important thing, to me, is that it would be interesting to hear the experiences of one who has been able to buy a 2023 Prius Prime. My local dealer says I might see one sometime next year. I am prepared to replace my car next year; the question is whether it will be with a new PP or a pure EV. Tell us how you were able to purchase your 2023 PP please.

 

You will have some technical issues with the way of your recording data and analyzing the cost. I rolled up the total charge (kWh) to the next gas fill-up because as you said, there is almost no way to separately record accurate HV mode miles (using a gas engine only) and EV mode miles (using the traction battery from the wall charge only). Unless you usually do 100% EV mode most of the time and use only HV mode on an occasional long road trip there will be some mixing of both EV miles and HV miles on your trip meter (or odometer whichever you use to track the traveled distance). Even in pure EV mode, if the engine fires during EV mode or you run out of EV range and then switch to HV mode before your next charging, you will have a mixing of HV and EV miles.

There is no easy way to separate those two portions of traveled miles. So, I decided to track the total cost (wall charged kWh + gas used) at the fill-up. This way, I can at least get an accurate overall cost/mile (gas and electric combined). But there is no easy way to separate gas cost/mile and electric cost/mile. You can make an estimate for each cost, if you keep track of miles/kWh recorded on the Eco Diary and Driver Monitor data (that is if Gen5 still offers the same function as Gen4). From the daily average miles/kWh, you can calculate the miles driven on EV if you know how much kWh charge was used.

I actually kept all of those data from Eco Diary and Drive Monitor both 1 and 2 and SOC used for each charge interval. So, for my 2021 PP after 12,678 miles, the estimate was as shown using the lifetime average EV efficiency value the car was showing on the Drive Monitor 2, which was 5.0 miles/kWh.