Ten Years On...A Dead Battery

So off to scenic Berkeley for dinner with Ted and Diane at an Indian Restaurant. Into the trusty but feeble Penny The Prius and off we go about 2:15 last Wednesday. Thru the canyon and down the hill into Vallejo Kelly drove in the fairly light traffic. We crossed the Crockett/Vallejo Bridge (Carquinez)and as we gained the other side and found ourselves on the uphill climb out of the bridge Penny gave a lurch and went into high speed engine mode with the Brake lite on and the check engine light still on from a few days before. Teh all manner of Dead Prius indicator lights came on and she ran slower and slower as Kelly pulled over to the right to get out of the flying traffic. We sat there a minute, she turned Penny off and then back on and away we went like nothing happened...but it HAD and shortly it performed the same set of tricks again, Kelly pulled over once again and turned her off and on and we headed south once more. Third times a charm isn't it? Yes, same thing about a mile further on. More Master Warning indicator, check engine and the racing engine and slow speed business along with it. Shit! So we decided to abandon dinner with our friends and return home and I would take Penny to the Toyota Dealer in Fairfield tomorrow. We turned around and she made it back to the bridge and I told Kelly we could still go to dinner...we'd just get Penny to the Toyota Dealer in Vallejo instead which was about 10 minutes away. I called the dealers number on our cell phone and asked about a rental car and told them of our Prius problem. They said they had one and we arrived a few minutes later with only ONE failure coming back. They took mu description and promised service the next day. We drove the 2010 Prii across the bridge and had a wonderful time and meal at the Indian Restaurant previously chosen by Ted and Diane. The next morning the dealer called and said they didn't have the car key! In the excitement of the moment I had taken it to remove some things from the back of Penny and place them into the rental's trunk...and put the key's into my pocket where I found them. Kelly was going to Vallejo shopping anyway so she dropped them off at the dealer along the way. About 11am the dealers rep called saying they had fixed the air flow sensor by cleaning it, had done to analysis of the codes and after checking the HV battery found cell #9 was not at the normal voltage. Than meant replacing the HV battery, a $3700 proposition plus the other repairs! She's our car, the only car we have outside of my trusty Ford truck...what to do?! Say yes and deal with it. I called back and told them to go ahead. They called later that afternoon saying the work was done and Penny was good to go once again. We picked her up the next morning and came home $3940 dollars lighter. Penny IS 10 years old, the California Emissions Warranty says 10 years or 150,000 miles whichever comes first. It IS September 2010...it's LIKELY she is 10 years old when the battery bellied up...but is this fair or should there be some pro-rated rate for the few possible months? I don't know...but when you Prius owners have battery failure...hold on tight! It's an EXPENSIVE repair!