2013 Prius Won't Start -12V?

I just replaced the wiper fluid reservoir in our 2013 Prius. This involves taking the front bumper cover off as well as taking off the headlight for easier access. I installed it, tested it, then started putting everything back together. I had to tighten down a wiper arm that had gotten loose as well. I tested that too and all was well. I changed a headlight bulb and tested it. When everything was back on I did one last check on the turn signals. I noticed at least one time, the headlights were staying on long after I turned the car off. Wasn't sure why, but didn't think much about it because they eventually went off.

Once I got everything put back together I went to start it to take it off the ramps and finish the job. Wouldn't start. It was making a whining noise and beeping like when you back up. The only lights coming on were the anti theft light and door open light. No radio, no other dash lights. The dome lights were coming on, but were low.

I assumed I had drained the 12V battery because forum responses seemed to be pointing that direction so I tried jumping it and nothing was changing. I checked the battery in the trunk and it was showing about 11V then I checked the voltage at the fuse box and it's only showing about 6V....

.....so here's an update to that. I just checked again and both the fuse box and trunk battery are showing 6V...is there a way I could have gotten the trunk reading to be 11V before and 6V now? I connected it to the other car to try a jump...while it was connected I checked the voltage in the trunk and it was showing 12V. I pressed the power button and everything lit up and the wipers started going so I thought I was home free. Disconnected the other car and everything went dead again. I did disconnect before the engine kicked in...if I had waited would it have possibly kept going.

I connected the other car again and did the same thing, but it was just dead. I checked voltage in the trunk again while connected to the other car and it was at 6V.

I have the battery disconnected now to see if the reset thing works, but I wanted to use this half hour to see if there are any ideas someone might have.

Thanks

 

Whew...well, it was the battery. It didn't want to jump off our other car, but it was happy with my friend's van.

Is the Prius usually picky about how it's jumped? The car I was trying to jump it from does have some extra adaptive equipment on it, but the battery was still showing 12V so I thought it would be good. Was the Prius maybe just seeing something it didn't like?

Thanks for jumping in with the helpful comments.