Battery issues and other problems

I bought my 2006 Prius a little over a year ago from a Toyota dealer in the area, and within the first month I had a strange occurrence. I got into my car, pressed the power button to start the car and everything on the dashboard lit up, the power button flashed amber, the clock's numbers were just barely visible, and the car wouldn't start. Frantic that no matter what I did (shut it off, took the keys out, and tried again several times with the same results), I called the dealer who sold me the car and just as he was about to send out a tow truck to get me, I tried it one last time and it started. I took it directly to the dealership, they inspected it, and came back with the response of 'there's nothing wrong with it, I don't know why it did that. If it happens again, come back again.' No charge and supposedly no problem, I let it go.

Well, exactly 1 year later (to the day) and suddenly it happens again. So I take it to the dealer again (which costs me a $55 diagnostic fee, so now I'm getting irked at this whole matter). They checked the battery in the back and now they're telling me it's a bad battery cell. They insist the two incidents are completely unrelated and that it will cost me +$500 to replace the bad cell. I left to go to class that night and had no more issues that day. But now I have a car that's been getting harder and harder to start. The power button doesn't even light up green anymore. I've noticed that I have issues when I open my door and the alarm goes off like I've left the key in the ignition, but I haven't. I knew when I opened the door yesterday and the alarm sounded that I was going to have issues. Sure enough, the car wouldn't turn on, and after two tries, it became completely unresponsive.

So I guess I have a few questions about this whole thing. Which battery has the bad cell? They tested in the back, where the hybrid battery is. But I thought the hybrid battery is covered up to 100,000 miles, so why is this going to cost me +$500 to fix? Also, it seems like there's something more serious than just the battery, considering I've read the manual a zillion and one times since I first had issues in hopes of trying to figure out what's been going on. The power button, like I said, flashes amber when it turns on, then disappears once it's on, but there is no green light instead.

Also, I've been getting repeatedly worse and worse gas mileage since the fall, the last fill only lasting me 350 miles or so with an mpg average of 34.6. I know it's winter and that the Prius typically gets worse gas mileage in the winter due to the heater being on. But the funny thing is, I don't drive with the heater on, even through the winter. I only use the heater when I need to defrost a window or I have company in my car because I like the cold. However, I got stuck on the I-90 for about 9 hours in the beginning of December and I noticed then (I had a classmate in the car with me) that the heaters for the feet was varying how much air was blowing out of them after a few hours, and ever since then it's had the same problem. I figured it might have been a need to change the cabin air filters, but now I'm wondering if it points to something else...

Anyways, back to the gas mileage issue...The first winter I had it, I dropped from a 52 average (my first tank of gas, the one I got from the dealer) to only 45-48, due to the sudden wind and snow we got the following week. It got somewhat better in the spring and summer, though I never did get back up to the average I did with the first tank of gas. I said something to the person who sold me the car, and he figured it might be the wind, but I kinda got the feeling he was uncomfortable, almost nervous, about my concerns after only 4 months of owning the car... (by the way, he quit working at the dealership where I bought my car the following month, and I've always wondered if there was something more going on behind that, but it's merely speculation...)

Often the engine kicks in as soon as I turn the car on to charge the battery, and I always seem to be running off of the engine more than normal since then too. Are these two issues, the battery issue and the gas mileage, related? If not, what else could be causing the terrible mileage? I just had my car aligned, 4 brand new tires, and a wheel bearing replaced. I had a steering joint that was making all kinds of noise within the second month replaced (for free, thank God, though they REALLY pushed to try to prove that they weren't responsible for the bill) I got a new filter, and I've changed my oil when the light has come on. If there is something else I could try to fix the poor mileage, I'd love to know...

My father has been quite upset that I bought a Prius for my first car in the first place, insisting all the time that it's a lemon and I should get rid of it, and I'm having a harder and harder time defending my purchase against him when I have more and more issues. I had to jump start my car yesterday for perhaps the 5th time since I had it, and frankly, I'm tired of worrying about missing something important because my car won't start that time.

Any insight into any aspect of this is very much appreciated. If more details are needed, please let me know, and I'll happily provide them.

 

Thank you all for your help. However, I've already called a few stores known to carry car parts and batteries in the area and all of them tell me that they are unable to order the 12V battery.

Is there a chain store that I might be able to purchase one from that would likely be able to order it?