Power at 12v no power at front terminals

[Accidently posted this same post in the newbie forum, though I would try posting in the correct forum!]
Hello PriusChat! Here is my situation:

The car has zero power to any electrical function, however, it can be jump-started from the from front terminals under the hood, and all the car will run as normal and display no diagnostic codes (at least according to my bluetooth OBD2 reader.) As soon as the car is turned off however it shows no power to any electrical function. I have searched through this forum but have not found anyone with the same problem that I have (although I could have missed something.)

Here is what I know so far:

-The 12v battery is good and only a few months old (displays 12.94 v across the terminals and the guy at Autozone also confirmed the battery is good.
-Across the terminals, under the hood, only 0.5v show up on my multimeter.
-I cleaned and tightened all battery connections and terminals, and voltage is reaching the end of the negative cable and the end of the 120a fusible link box on the positive terminal.
-The 100a fusible link at the front passes a visual inspection and reads about 0.05 ohms on my multimeter.
-Prior to this issue arising the car had been sitting at airport parking for about 6 days and the car had been resetting the clock and MPG after being turned off, and sometimes instantly restarting after being turned off for about two weeks. From what I have seen on the forums the issues that existed before the car stopped having power have been attributed to faulty grounding or a bad 12v, however, the battery is good and as far as I can tell the grounding wire from the terminal is securely attached to the body.
-My OBD2 reader is reporting 15.1 v when I have it jumpstarted and idling.
-The car I jumpstart the Prius from does not need to be on for the Prius to come back to life, the leads simply needs to be connected to the terminals in both cars.
-Trying to jumpstart from the trunk does nothing (which is to be expected if 12 volts are detected at the back but not at the front.

Information that seems less prevalent but may be important to someone more knowledgeable than myself:
-Some water has been pooling in the interior body paneling below the battery compartment.
-The 12v was replaced in March of this year by the previous owner.
-I have had this car for a few months but have put some serious mileage on it.
-Whoever replaced the previous 12v apparently did not replace the hydrogen vent as I found it down by the spare tire. I immediately replace it when I noticed this about a week before this issue came up.

My plan of attack is to continue to check relays, fuses, and circuit breakers between the front and back end according to wiring charts I obtained from this forum. Any advice or suggestions on where to look for blown fuses /lose wires / broken wires would be greatly appreciated!

Many thanks,
-Prius Bob

 

The 120a fuse passes a visual and voltage test, I am currently looking for a break in the wire but nothing has turned up so far.

 

I measured for from the negative terminal to the frame and got from 0.00v to 0.03 volts.