My dash is lit up like a Christmas tree!

I think I see what you did there. In Priusland, we use "on" and "ready" to mean two different things. You get to ON by pressing the button twice without touching the brake pedal. You get to READY by pressing the button once, while holding the brake.

I believe you went to READY and then looked at two voltages, when the engine happened to be stopped or running. 13.8 and 14.1 are both typical READY voltages. Unlike other cars, READY or not is really what matters, and the engine comes and goes as it pleases, and doesn't make much difference.

It is also good to have an actual ON reading (when the dash is lit up, but the word READY is not). That's not going to be in the same range. I'll believe it if it's under 13. That tells you more about the 12 volt battery, because in READY the voltage you see isn't coming from there.

When I mentioned the brake and transmission ECUs having strong opinions about the voltage, I didn't just mean you can see the voltage readings in their data lists (which you can). Those ECUs will in fact set specific trouble codes if they ever see the voltage go outside the ranges they like. So you can conveniently find out if they ever saw that happen (and if your scan tool is able to retrieve freeze frames, you can see exactly what the voltage was at the moment the code was set).

Yes, that's going to be your main headache. The whole reason they invented C1451 is to keep the system on strike until you get through a brake bleed. Nothing else will clear it. You've no doubt already noticed that a general code clear will not. Neither will disconnecting the battery—that clears nearly all codes in nearly all ECUs, but C1451 is nonvolatile. Until you have access to a scan tool able to complete the bleed procedure, you are stuck with fail-safe brakes.

I told you that code makes me crabby.

You don't even have to really open the bleeders. If you never opened anything or let any air in, you can just click Next Next Next through the bleed procedure until it's done and never touch a wrench. But you have to get through it.

 

Those readings are NOT the voltage of the battery itself.
That is the charging voltage and has no bearing on whether the battery is good or not.