Highlander Hybrid electrical issues

Greetings. I recall encountering a somewhat similar predicament with my previous vehicle, a 2018 Opel Insignia. The symptoms manifested as erratic electrical behavior, accompanied by diagnostic codes indicating voltage irregularities. Have you by chance assessed the condition of the alternator? An underperforming alternator might contribute to battery discharge, consequently inducing overvoltage occurrences as the system endeavors to compensate.

Interesting. I haven't checked the alternator specifically. But if the alternator was failing, wouldn't the car just not charge the battery at all, instead of overcharging? I am not fully grasping the connection you are describing.

Indeed, it is a subtle interplay. An alternator operating sub-optimally might exhibit inconsistent voltage regulation. This inconsistency can lead to sporadic overvoltage incidents, particularly when the system attempts to rectify a perceived deficiency in the battery's charge level. While I lack the resources to provide definitive diagnostic advice, I strongly suggest seeking counsel from a qualified automotive technician. Such matters necessitate meticulous examination.

Thanks, that's helpful. I appreciate you sharing your experience. Took it to the shop, and you were right. It turned out to be a defective battery. Replaced it, cost me 290€, and everything seems to be working fine now.