How I found out my 12 volt was dead and my hack to get my car going

I have a 2005 Prius . The other day my wife called said the car has no power it was showing the

 

So we got the triangle of death and dead hybrid battery light and engine light all came on . I was thinking crap this will be expensive . I had a very large marine battery and jumper cables . So to see if it was the 12 volt and not the big hybrid battery I put my jumper cables on the battery in the trunk . Effectively making the Marie battery the replacement and when I turned the car on everything worked all lights went off . Except the check engine light .I drove the car for a long drive 30 min or so and came home turned off car and restarted all warning lights went off telling me it was the 12 volt . I drove to town bought a new 12 volt from my local shop . Everything is good. I noticed when I put the new 12 volt in my car did not run the gas engine as much I think it’s been trying to boost the tired old 12 volt for some time . Now the car works like new again and even stays charged with green light longer . Hope this can help someone

 

I was not trying to boost the car . I was trying to determine if it was the 12 volt was the problem and by putting a battery connected to the terminals will effectively be like I have replaced the battery and told me that was the problem and allowed me to drive my car to town and get the proper battery