HV Battery Cell Replacement

how old was the 12v?

i would replace the bad module

 

My opinion (and we all know what that is worth!!) is there's nothing to hold them accountable for, other than draining and recharging the 12v battery. The work they did should, in no way, cause a module in the HV battery to fail. This one falls under coincidence. One of the modules has a failed internal cell. After the first failure a year ago, you should just go ahead and expect an annual (or more frequent) rebuild cycle, as the other modules are still original 2007s. If it goes more than a year that's great, if it goes 2-3 months before the next failure, it's not unexpected or unheard of. Unless you have the equipment to get an accurate assessment of each individual module, it's practically impossible for someone to optimize the battery.

 

I recognize that 95% of Prius owners know very little about the electrical portion of the car. Probably 4% have a reasonable understanding of the electrical systems. <1% probably have enough electrical background to comfortably and confidently understand the systems. Probably less than 0.1% are FULLY capable of understanding all the systems. I would consider myself to be somewhere near the 1% group, having spent 30+ years in electrical and electronics fields.

Think of the HV battery as a bedroom with 28 light bulbs. All 28 bulbs were installed 12 years ago. You're in the kitchen making dinner and turn on the oven light to look at that killer roast you're cooking. Everything is great, so you head to the bedroom to put on some PJs for the night. You turn on the bedroom lights and one is burned out. The chances of anything outside of the HV battery case causing a module to go bad would be about the same as if turning on the oven light caused the bedroom light to be burned out.

And yes, that one failed cell that causes the 1.4v difference is exactly what the Gen 2 system is supposed to detect.