[2023 Prime] Watts, Watt-Meter, and Not What

FWIW, the LCD screen on my Poniie watt–hour meter went blank after about five years. I should have bought a name brand.

 

Level 2 charging at 240 volts is much quicker and significantly more efficient!

 

Even better, don't worry about it!

I would be more worried about charge scheduling, timing, and limit to preserve battery capaciy.

 

For those who like numbers, here is some useful information about the high voltage battery in my 2024 Prius.
Toyota keeps safety margins to protect the HV battery, the bottom margin is 14% SOC and the top margin is 11% SOC.
This means that the battery is used from SOC of 14% to SOC of 89% when the dashboard indicator indicates from 0% to 100%.
So, we only have 75% of the 13.6 KWh available, this gives 10.2 KWh usable.
For maximum longevity of the HV battery, it is recommended to use it between an SOC of 20% and an SOC of 80%.
We obtain a SOC of 20% when the dashboard indicator gives 7% and a SOC of 80% when the indicator gives 87%.
So, looking at the dashboard indicator in % mode (not in KM or Mile mode), if you want to use the battery between 20% and 80% SOC, you should use it between 7% and 87%.
Being below 7% for a long time damages the HV battery and being above 87% for a long time, especially when it is hot, also damages the battery.
It is still recommended to charge the battery to 100% (SOC of 89%) from time to time for balancing the cell voltages which is carried out by the HVB (BCM) when charging from 90% to 100%.
This is why the last 10% of charge is longer because the controller will discharge the cells whose voltage is too high so that all the cells are at the same voltage.
For those who want to see the SOC value of the HV battery, you must use an OBD2 scanner or an OBD2 dongle with software like Carista.
It is possible to display the SOC value in real time on the infotainment system (Android Auto) using a dongle combined with the Torque Pro and AAtorque software and/or Performance Monitor.
As for performance, here are my values obtained.
When charging on a level 1 charger, the first 10 hours gives the dashboard indicator in % mode (not KM or Mile mode) 9% charge per hour and the last 10% takes 1.5 hours due to cell voltage balancing, so a full charge takes 11.5 hours.
To recharge the Prius Prime for one hour on a 120 volt network, we consume 12 amps, therefore ~1.4KwH.
But this 1.4KwH only gives 0.9KwH on the battery (100% = 10.2Kw/h).
This is because there is a lot of loss caused by many of the systems required for charging, including the DC-DC converter for 12 volts, the HV battery charger, battery heating or cooling, the battery management system (BCM), thermal loss, etc...
So, we obtain a return of only 64% for the first 90%. (And 45% for the last 10% because of cell balancing)
If we put electricity at 12 cents per Kw/h and don't look at losses, the first 90% would cost $1.08.
But in reality, the first 90% requires 10 hours at 1.4Kw/h which gives 14Kw/h at 12 cents per Kw/h we get $1.68.
Note that on 240 volts (level 2 terminal), the losses are lower compared to the energy supplied to the HV battery.
In level 2, 240 volts at 16 amps gives approximately the 3.5Kw/h displayed.
With the losses of 500 watts we actually obtain 3Kw/h.
For a full charge, we get 30% charge per hour for the first 3 hours and 10% for the last 30 minutes (Due to cell balancing)
If we put electricity at 12 cents per Kw/h and don't look at the losses, the first 90% would cost $1.08 as before.
But in reality, the first 90% requires 3 hours at 3.5Kw/h which gives 10.5Kw/h at 12 cents per Kw/h we get $1.26.
Note that the last 10% charge is always more expensive and is not recommended to be performed every day.
So, a level 2 charger is more economical than a level 1 and, EV mode is even less economical than we think because the nomenclature does not talk about losses...
Have a nice day.