New prius Prime with dead 12v battery this morning

I left my blue 2021 Prius Prime Limited, almost three years old now, left undriven and garaged in hot weather for almost six weeks. No trickle charger was connected. This is what happened:

1. PHEV battery SOC was 24% when I left it, and it was still 24% when I restarted the car after six weeks. (I chose 24% as the optimal lithium-ion battery storage SOC.)
2. There were no 12-V battery issues. The car started fine. I then charged the PHEV battery, and then the car started fine again.

I think the 12-V battery system in Gen 4 Prius Prime is great. Here is why I think some people have issues because of the following improper maintenance:

1. Repeated short trips and few long trips. This does not allow the 12-V battery to fully charge. You should do at least one trip of ten–fifteen miles or longer every week.
2. Use of the Accessory mode. You should never use the accessory mode but always use the READY mode instead.
3. Sitting in the car with the car not in the READY mode. This causes the 12-V battery to drain because the lights are still on etc. Never turn off the car until you are ready to leave the car.

 

Do you have an active Telematics subscription eg. Remote Connect, Safety Connect?

 

Yes, I do.