I have a battery problem on a 2020 Prius Prime

…no, not that battery 😉 the standard old 12vdc battery and charging system that powers the vehicle accessories.

The six month old 12v battery completely discharged when the car was left unused for only 5 days and the car was connected to a traction battery charger for that entire time.

So, I’m trying to track down why the battery failed.

I found Torque’s 12v voltage parameter and assume that I can start a log watching that value by leaving an old phone with torque running in the car. Anyone have any experience with a quest such as this one?

The second value that I would like to watch is the current draw from the battery when the car is not in use and turned off. I strongly suspect that Toyota is allowing something to consume current from the 12v system.

I didn’t find a “current draw” value in Torque, and I further guess that Toyota does not provide this value to ODB2. Again, anyone have further info on what my options are?

Thanks in advance for any and all thoughts,
Beverly Howard

Well, most of the day has been learning a variety of things, both about the car and now the current version of Torque

Some Torque questions I assumed would be easy based on past experience but I’m now lost.

How does one start and configure logging with the current version? I have successfully set up the “line graph” and that is showing the battery voltage information as I need, but I have been unable to find out how to “log” the same data to storage.

What I have been able to find searching is that line graph is one of two logging options

Thanks in advance,
Beverly Howard

…and if it tries to communicate to the ECUs it will also stop the car from sleeping

Thanks for that “heads up” …appreciated.

The OBD2 port is powered with the car in the “Power OFF” state, and the adapter shows the two voltage level readings (Voltage Control Module and Voltage OBD Adapter) available that I am looking for and with more accuracy (0.1v) than I need for this quest.

I’m looking for evidence of sudden 12v battery voltage drops from something switching on. In addition, I’m trying to document the system behavior with the traction charger attached and disconnected.

It appears that leaving the charging connector connected after traction battery charging is completed creates a scenario where the 12v battery will be completely discharged in less than 5 days.

Both of these voltages are available to Torque in the OFF state and, so far, I cannot see any evidence that watching these via ODB2 has activated any other functions or battery consumption.

I’ve also been careful to keep the keyfob out of range during all of this snooping setup and learning process.

Thanks again,
Beverly Howard

bevhoward, I think your car’s ECU should provide information about the status of your battery 12 volts, you need to use external PIDs

i’m no prius pro

but i think i heard that there was some issue with the prius electrical logic, if i remember correctly

if you only do small ride on the main battery

the dash and internal electrical stuff is powered by the 12v battery… but the car is not smart enough to start the engine to recharge the battery in those condition

so i would not be surprise if there is some other logic flaw