Prius II Lottery Loser (battery issue)

Major Update. My friend charged and discharge the three cells over the weekend. Monday night he came over and hooked them up and we balanced the cells until tonight. Tonight we swapped the three cells in the pack, and re-assembled it. We placed the pack back in the car. When I pushed the Start button all the normal lights lit up but the Ready light did not come on. I pushed it again and then it came on. The battery level showed strong battery, like 6 bars and it did not waver like when we took it out. The ICE kicked on and it showed it was charging the battery. That lasted probably a minute then the ICE turned off. We hopped in and took it for a spin. We drove for about 20 miles and by the time we got back two more bars lit up (all but one) and it was showing green bars. Also, it showed like 55 mpg over that time period. It was mostly highway driving but it was up and down some hills. I can say that I don't ever remember getting that good mpg over that type of driving.

So, my friend takes off and I take it out some more. I need to get gas so I drive into town. Filling up resets the mpg monitor. So, from the gas station I go four miles north, travelling about 30 mph and I only hit one stop light but I show like 97 mpg. It appears flat but it must be slightly downhill. I head back the way I came so I can do a full test. I end up four miles later with 77 mpg having completed the round trip. I'm thinking this battery is strong.

I'm going to drive it for a few days and then I'll report back. My first impression is I will see a gain in mpg. I normally get almost 46 in mixed driving. At first glace, I'm thinking I will see over 50 mpg.

I think I'm into this about $400 at this point and that includes $100 for Toyota diagnosis and $100 for car rental for four days.

 

I wanted to report back now that I have put 1500 + miles on my fixed battery. I'd say that I'm getting slightly lower mpg than what I used to get. I used to chase 46 mpg now I chase 45. My normal drive to work is up/down hills for about 7 miles, I might go out to lunch, same thing. Not many freeway miles. I will say this car is pretty amazing. When I do drive freeway or more extended miles in town it will get 52+.

I am looking for another car now but just haven't found what I want yet. The friend that helped me fix it is wanting to buy it but he's in no hurry so I can take my time.

Thanks everyone for your help and advice along the way.