I'm a new member also. I have a 2005 and yesterday the master warning light came on. I went to the dealer and they checked it out. They showed me the voltage readings on the hybrid batteries and all were about 14.1 v except one which read about 0.5 v lower than the rest. The dealer determined that I needed to replace the hybrid batteries for a smooth $2800. Interestingly on my way home the warning lights all went out and everything seemed to be normal. Now I'm wondering what to do. Obviously I need a second opinion. Should I be concerned about the one cell's lower readings?
Oh boy, where to start. The traction battery cells are 1.2VDC each - not 14.1. There are 168 NiMH cells in the 05 Prius assembled in 28 modules containing 6 cells in each module. The module voltage is 7.2VDC. What diagnostic trouble codes (DTC) were stored when they inspected your car? Did the stealership even bother to tell you what they were? They should have been listed on the work order you signed and paid for. If not, call them and ask for any/all DTCs they found and lettuce know what they are.
You might want to consider if your regular 12v battery is in good condition. I am not a HV batt expert, but it is true that one bad module can bring down your Hv batt. Although it is theoretically possible to fix the one bad module, it is a lot of work to rebalance all of the cells, so normally, not done. If HV repalcement is deemed necessary, you could replace with a reconditioned batt, salvage batt or new Toyota batt, the latter being the most expensive option. Even a good quality reconditioned batt (Re-Involt.com) is probably going to run you $2000. Good luck.
If the warning lights have disappeared and not come back, their is a possibility that this was a temporary condition. If this were me, I would drive it and wait for the warning lights/DTC's to come back (consistently).
They are talking about block voltages (14 blocks per HV Battery) The battery ECU, which monitors two modules as a single battery block, detects the battery block voltage at a total of 14 locations.
I second wjtracy's comment to check the 12V battery. If it's bad, all sorts of strange codes can be stored. The HV battery probably does have a bad cell, but that's a big hit to take before making sure that the 12V isn't the problem. I think it's about $2000 for a Reinvolt refurbished battery installed.