High voltage traction battery - recalibration - fixed

Some info that might help other Gen 3 owners.

I almost bought another HV traction battery believing it was weak at 100k miles. There were wild swings in the state of charge and unexplained overshoots below 40% and above 80%. I figured out how to recalibrate the computer which seems to have put it back to normal.

About 2 years ago I received my car back from a Toyota software update and noticed the traction battery wasn't quite right. I was starting to experience wild swings in the state of charge. This is normally a sign that the battery was weak and about to fail. I was closely monitoring pack voltages and could see state of charge count down in front of my eyes from just sitting parked with the car on. The engine would then kick in to recharge the battery, but the weird thing is after normal driving it would overshoot 60% and hit 80% very quickly and start the engine again to drain the traction battery.

To fix it, all I did was find a nice gentle hill and glide down it to charge the battery until it reached 80% state of charge. Then I disconnected the 12v auxiliary battery to reset the computers. I then let the car glide further down the hill until it reached 80% again, then reset again.

For the last 5 months now it seems to be back to normal. Somehow the battery ECU was recalibrated and the whole system is working like new again. Pack voltage delta is back to a healthy 50mv.

If you have a weak traction battery, try this trick and tell me how you go.

 

When you disconnect the 12v battery to reset the battery ECU it also resets the state of charge back to 60%. You can then give the pack another 20%.

State of charge is a combination of coulomb counting and max voltage. After a bit of normal driving it seems to figure out the pack capacity and adjust accordingly.