Parking brake lock and low battery

So, I got the Red triangle and P lock malfunction, go on flat surface, etc.

Turned the car off, tried to turn back on, wouldn't. Jumped it, it turned back on. Did the wire from fuse to blue wire, which reset the parking brake, and allowed me to put the car in gear. Red Triangle of death was still there.

Next morning, triangle is gone, car functioning normally.

When I check the diagnostics of the car by doing the info/headlights x3 thing, it shows 11.8-12 volts, yesterday on the lower end, today it's staying at 12 or 12.1v.

Then when I press power button again to put a load on it, it goes down to 11.8-11.9.

When I turn the car on, it goes to 14.7-14.8.

Is anyone able to help me diagnose this, because I have no idea what I'm doing. Should I put in a new battery, or is this some kind of issue with a hidden draw on the 12v battery happening?

This thread says with the car on, it shouldn't go above 14.4 or there's an issue.
There is a problem with the transmission 'P' lock mechanism...... | PriusChat

 

Only 2 years old, and it's an Optima. So if you're saying I need a new battery, leads me to believe I've got a drain of some kind happening. Lame.