I'm looking for any patterns in module failure. Is it random? Closer to the ECU? Toward the middle? (fan is to the right, the opposite side of the ECU, in gen2 FWIW). Also ever had any fail right on an outside edge before? Thanks!
If it wasn't such a PITA it would probably make sense to rotate the module positions periodically so that on average over time they all are exposed to a similar temperature profile. That would probably keep the pack in balance a bit longer. In this world though it is a PITA and it doesn't really make sense to do all that work at the needed intervals just to eke out another 10% life on the pack, which will pay off, maybe, a decade later. I hope and suspect that liquid cooled packs in EVs have less of a problem with varying temperature profiles. Certainly they are much better than air cooled packs in this regard. Or at least the Nissan Leaf demonstrates that air cooling an EV pack is not a great idea.
Just for fun I looked for images of "Dr. Prius" to look for temperature readings of the batteries and sure enough, usually temp1 is coolest, temp3 is 1 degree higher than that, and temp2 tends to be 4 degrees (celsius) higher than that... And I also wish somebody would make an aftermarket module case that allowed hot swapping easily...
I'll collect random reports in this thread. Here's one of somebody losing a cell in the middle of the pack: Changing bad module on hybrid battery without balancing? Please help! | PriusChat here's another with two from the middle: Gen II Prius Individual Battery Module Replacement | PriusChat here's one from the middle but interestingly the two "right on each edge" are also weak: Gen II Prius Individual Battery Module Replacement | Page 3 | PriusChat also end ones "weakened" mentioned here Gen II Prius Individual Battery Module Replacement | Page 57 | PriusChat (and another middle failure). Another mention of #1 and #28 being weak here: Gen II Prius Individual Battery Module Replacement | Page 86 | PriusChat another middle dead with end weird here: while i have the HV battery out of my gen1 | Page 6 | PriusChat another with a dead middle, ends weird: Replacing Modules | PriusChat I haven't heard of the ones on the end actually dying though, just being more degraded (?) I may have had some luck doing a recondition on one before FWIW...
Sure enough "temp1" is the one farthest from the ecu, i.e. closest to the fan in my 2007 https://priuschat.com/threads/what-order-are-the-hybrid-battery-temperature-sensors-in.251473
