Homebrew charge tracking: is this feasible?

I've posted elsewhere that I am less than impressed with Connected Services and its reporting on my 2024 Prius Prime's charge history. Connected Services has now expired, I'm not going to pay $ for that quality of product, but I'm curious if it's possible to create a home-brew rig to replace the charge history.

Parameters: I am a professional software engineer; computers, networks, and data do not scare me. I am a relative newbie to automotive systems, however, so there are places where I don't know what's possible or how difficult it may be to do.

This is the plan I kind of mapped out in my head:

1. Add a small network-enabled computer to the Prius Prime which can connect to my home wi-fi network. (Something like a Raspberry Pi.) This computer would sleep most of the time (don't want it drawing power) but would wake up and dump data at a fixed time of day (probably early morning) or on specific triggers (like returning to the home WiFi network after being out). Time-based reporting would be pretty easy; event-based is a little trickier, but not impossible.
2. This computer would need to read data from the Prius Prime. I am hoping something like a Bluetooth OBDII interface would allow this to happen with a minimum of wiring-harness shenanigans, but this is where my lack of knowledge comes through: I don't know if the data I'm after is accessible through ODBII.
3. I'd need an API service running on a host in my network to receive and store the data. (This is the part that's actually easy for me; I do this stuff professionally, and I can visualize a service running on my existing NAS which would receive data dumps and provide some basic reporting.)
4. Ideally the "cleanup" would include disconnecting the Prius Prime's cell antenna so the data is no longer reported to Toyota. (I know this is not a widely-shared opinion, but my position is that if I actually own this car, I should have control over where its data goes.)

How much of this is pie in the sky? Is battery charge data available through OBDII, or would I need a different data source? Is there an easier way to do any of this? Has anyone tried anything like this? (...why not, given the vibe I get from this crew?)

 

OK, this is helpful. It looks like the battery SOC is going to be the data point I can work with; I'd need to watch for events (like changes of charge state) and snapshot data at event time. I was visualizing working with a reader like this:

OBDLink® MX+ - Outstanding Bluetooth-Compatible OBD II Scan Tool

...but not necessarily that one, that's just the class of reader I had in mind. I'd need to verify it's small enough to leave plugged in, and I'd need to figure out a location and power supply for my on-board data caching computer, and make them talk to each other. I think those would be the hard parts. Dumping data from the caching computer to the home NAS would be easier.

I could probably get a RaspPi (or similar nano computer) and OBD reader without breaking the bank, and do some experiments to determine if the whole project is feasible.

 

Ironically having it on my phone would make it *harder* for me - I don't speak (m)any languages that run on an iPhone. But the transport layer (Bluetooth) is the same - the OBDLink folks had a developer (or developers) who wrote a phone-compatible app to consume and display the data coming in over Bluetooth. I'm proposing doing something similar, but using a more flexible platform I understand better so I can get the data where I want it. I'm not a consumer app developer so my product will be significantly jankier than theirs... but hopefully it will do what I want it to do.

 

I mean, the real jackpot would be getting access to wherever Connected Services is caching data before it's sent over the cell antenna, and just tapping that data flow, because obviously Toyota has already solved that part of the problem. (Also, based purely on rumors I've heard, it's probably not even sent encrypted.)