12V surprise

Sounds like the ECU settings were lost, and the car needed to relearn the best settings for fuel, climate, and driving style.

 

apparently OEM 12v battery lasting 5+ yrs. Car bought in 2019 Sept. Just had it checked 5yrs/3 mo later, still has 82%. just hope it just doesn't suddenly collapse.

 

The danger of having an exposed positive and negative connection near your battery terminals would make this a high risk proposition. Also, there could be a danger of arcing when connecting the jumpered connectors up to the new batteries.

Having had to replace the display unit in my 2018 Prime, I am EXTREMELY careful with anything to do with the battery. FYI - if you reverse the leads on your battery charger or cables, one of the very first things to blow out is probably going to be the display unit. According to Toyota, there are fuses inside the display unit that are replaceable but I wouldn't count on it. My issue was my head unit just died for no apparent reason. Toyota quoted me $9k (!!!!) for a replacement display unit and about $1k in labor. Luckily I found an independent Toyota Master Mechanic who swapped in a used unit that cost me about $1200 and about $500 for labor.

 

Any prelim. probs with head before failure?