Full failure in that something is literally broken with the battery cooling.
There is a loop that goes Diverter, chiller, pump, filter, on-board charger, battery heater, battery, return.
The diverter allows the coolant return to either go right back in through the chiller or dump out to the rest of the system and bypass the chiller on the way back in. Depending on the outside temp the vehicle will use the radiator to drop the temp instead of using power and running the AC compressor to cool.
During charging, the on-board charger is dumping heat into that loop along with any battery warming. Because my diverter failed in the position that bypassed the chiller, the loop would heat, get past the temp where the radiator can't get it cool (most of the time in AZ) and the car would start running the chiller, which was still being bypassed. Even better, the AC would be pulling several kW from the wall, which had to go through the on-board charger which was dumping MORE heat into that same loop.
If you suspect you have a similar failure, you may be able to test. There are bubble tubes that connect to the coolant reservoir and during normal operation they will dribble a small amount while the pumps are running. Since the bubble tube is behind the pump, you can set the diverter to go through the chiller and ramp up the pump a little. Then you can pinch the hose that's coming out the bypass side (the one that shouldn't have any flow, not fully closed) and see if the flow from the dribble hose increases.
If the diverter is positioning correctly, there should be zero change. If it increases, that means coolant is flowing in the bypass when it shouldn't be and pinching the hose is forcing it to go through the bubble tube for lack of a path out. You can do something similar on chiller return to confirm the diverter is not stuck in the middle, as well as on the battery loop itself to see if the impeller or filter are having issues.
I'll see about typing up a guide for this.