Troubleshooting 2007 Prius battery issue

replaced with what? a new oem, or some aftermarket piece of junk?

for a proper diagnosis, you need to scan the trouble codes with a proper prius reader like tech stream or dr. prius at the least.

 

Got the triangle of death and other dashboard lights lit up replaced auxiliary battery car started everything seem to be fine and then all of a sudden the triangle came back on does anybody know why

Sure....

1. Got the triangle of death and other dashboard lights lit up..the car detected a problem and is letting you know
   
2. replaced auxiliary battery ...have no idea how #1 led you to do #2. Did any codes get read prior to installing new 12v battery? Hopefully you have access to a scanner capable of communicating with all prius systems. Hybrids are picky.
   
3. car started everything seem to be fine...this typically happens after replacing a 12v battery, usually when a power saver isn't used and the 12v system goes totally dead. It wipes out all the 'short term' memory in the car ecus and they go back to factory default, which means no DTC codes are stored
   
4. and then all of a sudden the triangle came back on....because now the "default value" ecus are relearning everything about the car and they found out there is still a problem.

That should wrap it up.

 

Brand new battery and tests 100% healthy. Car starts and runs GREAT every day for about a week. Then, roughly once a. week, it won't start but after a jump, it starts up and keeps running for another week.

What could be causing this?

 

Did this start after the new battery was installed? If so, I would recommend checking all the connections at the battery and where the (-) cable fastens to the car body. Also verify the connection is tight and voltage is good where the main cable fastens to the fuse box (the underhood jump point)

If this is a problem that existed prior to the new battery, I would still check all the connections, but also start looking for something that may be a parasitic drain. Keep a meter in the car so you can immediately take some voltage readings at the underhood jump point and battery if the problem occurs.