Prime 2023 12V battery integrity on EV

So, AGM batteries are not immortal after all.

 

Reading about it, the main advantage of AGM batteries seems to be lower self-drain, ~ 2% per month vs. ~ 5% per month for a calcium battery.

AGM batteries seem to have shorter longevity vs. properly maintained flooded-cell batteries.

Does the self-drain advantage matter given that Gen 4 and Gen 5 Priuses have a high standby drain? Probably not. That would explain why Toyota might have opted for a flooded-cell battery, especially given the higher cost of AGM.

 

Thanks for this. I am newxto Prime, but had a few Prius. What is READY mode? I have EV, HV, ECO, sport, and a hundred menus to go! But I have never ever seen anything called READY. Can you please share how to set and know that a 2023/2024 Prius Prime is in READY mode? I have a 2024, bought in March 2024, with 9,000 miles. Today, March 4, 2025 it is being towed to dealer for a dead battery.
I do hope I get a battery and not just a charge and hand it back to me. My driving habits are all electric around town to get grocieries and an occasional road trip.

 

When you press the START button and brake pedal at the same time the car goes into READY mode. It charges the 12 volt battery in this mode and also any time the car is plugged in.

If you press the start button once the car goes into ACC mode which can quickly deplete the 12 volt battery.

 

The car has four power states. It's actually the same as your old Prius. That also had a READY mode that you used every time you drove the car.

1. OFF - self explanatory
- press power button once without pressing brake
2. ACCESSORY - some electronic components are on - radio, etc.
- press power button again without pressing brake
3. POWER ON - all electronic components are on
- press power button again without pressing brake
(back to OFF)

(from OFF)
- press power button while pressing brake pedal
4. READY - car is fully powered up and ready to drive


Here was your old Prius display. See the READY in the lower left corner?

And here's your gen 5 display with the READY on the left side in green:

 

Ready is akin to turning the key on an old car as far as it’ll go, activating the starter motor and the engine’s running. The Prius is similar except once engine’s partially warmed it’ll start shutting down periodically and so on.

 

It is less complicated than the explanations above.

READY = hybrid system on
(as indicated explicitly on the display)

The car cannot be shifted to gear or driven unless it is in the READY mode (= the hybrid system is on).

 

My battery was dead after almost a year last April 30 2024. The dealer tested the battery, deemed it defective and replaced it.