'o2 help Prius

12V is def not good. Don't trust the dealer on that. What are the codes and subcodes? Call the dealer and ask and post them here.

 

Get a mini VCI off Ebay + a laptop that runs windows xp or windows 7 32bit...Read codes and sub codes, it will give you a complete picture of your hybrid battery Modules and look into the voltage difference between adjacent modules, If they are different more than 0.2 volts then there is a problem...you will be able to see which modules go south when you put a load on the car (driving in reverse up hill )..Keep your laptop next to you and pay attention to these bad modules, note down these bad modules numbers and then you will have to take the battery off after removing the orange safety switch...Take the battery cover off and remove the bus bar that's been hold to the modules with 8 mm bolts. Get 4 Imax b6 chargers off Ebay....Discharge every battery cell to 6 volts at 0.7 ah....Then charge them back at 6 amps till they become fully charged with capacity cutoff at 7250 mah....Replace the bad modules with salvaged ones off Ebay and do the same discharge /charge sequence. The whole procedure should be repeated 3 times but 1 time can get you back on the road..Connect everything back....Mark bolts as you remove them. Be very cautious as it's a high voltage battery and you have to be electrically inclined to do that on your own. It's a doable process , I have seen it twice bringing 2 dead Prius back to live, till I finally did it on my own and revived my battery to optimal results. Good luck!!

 

You can easily recharge it yourself with a R/C Car charger, after dismantling it. I Used a Tenergy charger ( UPC: 851197001307 )

It takes a few hours per cell, but you will NEED Class 0 Lineman's Gloves. The battery can easily kill you if you aren't careful.

That being said, it isn't an unnecessarily hard job to do and the construction of the battery pack is designed for the safety of qualified technicians.