Prius won't go into ready mode after replacing 12v battery

The other day I started my 2005 prius and after driving a few miles I got the red triangle and pulled over somewhere safe to try to diagnose the problem. Upon turning the car off and on again it failed to go into ready mode, so I checked the diagnostic mode and the voltage of the 12v was fluctuating within the low 11s and high 10s so I decided that it was pretty much dead. I replaced the battery but the same problem still persists and I can't get the car to go into ready with the new battery resting at about 12v-11.9v. The brake lights also work perfectly fine so I'm pretty clueless on how to proceed.

 

I tightened the ground from the negative terminal which was a bit loose but I'm still having the same issue. The battery is currently reading from 11.7-11.9v depending on what is being powered. What voltage does the battery need to start normally? >12v? Also I never touched the orange disconnect and it seems to be properly in place. I don't currently have a battery tender so I'm going to go out and buy one now

 

Scraping off the corrosion from all the connections seemed to do the trick! Thanks for all the help.