Start with corrosion in hybrid battery ECU and battery wiring... After that test the battery modules...
I would think age every generation two I've had here has extensive corrosion on the bus bars and nuts they were once copper now they're black almost every unit that's been pulled into this driveway I look. The nuts are frosted with what looks like sugar from frosted flakes can't miss it You touch it you can feel it and the black on the bus bars you can just see when you undo one you see the copper rings where the nuts were squeezed that need to all be copper again or new same with the nuts All that green crap on the silver ends of the orange wire where they're crimped need to be cleaned up chemicals whatever makes a huge difference just that alone let alone balancing all the modules and ripping out ones that are no good but I've never seen a generation too with a clean set of connection going down either side of the battery even when seven or eight months old this will start the corrosion that is I don't think it's necessarily from water I just think it's from being outside and in the weather and all of that these things aren't sealed or anything like that moisture and weather just flows right through the case.
