RTOD – how bad can it be?

My first chat post. Please be nice.

2007 Prius.

3/24/2024 96,385 miles: HV battery was replaced with a new Toyota battery
4/22/2025 125,840 miles: the RTOD with P3000, P3020, B1421
Battery Block 10 weak
7/7/2025 133,352 miles: the RTOD with P3000, P3020, B1421
7/10/2025 600 miles later: same DTCs again
7/10/2025 40 miles later: same DTCs again

OK, so I’m starting to pay attention. Block 10 voltage is 15.80. Next (lowest) is block 4 15.99. Highest block voltage is 16.16.

Is it the “red triangle of death”, or “doom”?

What should my next steps be?

Thanks and regards,

Jim x 3

 

Thanks for your reply.

I don't have any secrets here - what can I add?

I purchased the replacement from a Toyota dealership parts department. The part cost about $1950 with a $1300 core charge. I did the work myself. I'm not an auto mechanic but I had the requisite tools. I am a professional electrician - the system design was well understood and the swap was straightforward with no surprises. I picked up the new battery in its sarcophagus on a Friday and did the swap over a weekend. The sarcophagus on the pallet does fit in the hatchback with the rear seats down.

The car previously belonged to my parents and it did not do well since they were old and did not exercise it regularly. My impression is that a 2 or 3 months interval between uses is death for this car. They are now gone. Conversely, my daily commute is about 75 miles 1-way. Almost all of that is freeway miles at high speed, 55-85 mph with frequent accelerations and decelerations for traffic. Cruise control is never possible. My mileage has been consistent and good - about 43 mpg.

Since there was a simple 1 year warranty, I didn't think it fair to ask Toyota for any consideration.

What else do you need to know?

regards,
Jim x 3

 

Thanks for your replies.

Trouble codes were in my first post.

I don't believe the installation has contributed. Aside from the battery weight, the installation was pretty easy (as compared to replacing the ABS actuator/accumulator). Knowing the design and history here, my feeling is that I've probably got 1 bad (weak) module in the block 10 pair and the rest of the battery is good. It seems a shame to now replace the entire battery again (per Toyota policy). Its also clear the car is operationally dead until this is addressed.

The internal resistances in each block as reported out by the car are all 24-25 milliohms except for block 10 which reports out at 34 milliohms. I didn't get a reading of the internal resistances when the battery was first installed. Does anyone know what these values should be?

I'm not adverse to disassembling the battery pack to replace 1 bad module, but I would need a new, not used, module for this.

My expectations for the battery were more than 13 months as well. I thought perhaps my daily aggressive freeway driving was somehow a contributor to the failure.

Regards,
Jim x 3

 

I must confess I've been in denial that this was and would become a chronic problem.

In April when the RTOD came on I was on my commute home. I stopped at the closest auto parts store since I had no idea what the trouble was. "Battery Block 10 becomes weak". I drove home, about 45 miles, with the RTOD in the dash. The commute had been on an especially hot day, with a mix of high speed driving and stop-and-go. With the RTOD the battery ventilator came on high. Otherwise the car seemed to drive normally and I noticed no abnormal behavior. At home I checked block voltages and internal resistance values. I reset the codes and hoped. For a while the problem seemed to have been a one-time issue.

In July, on 7/7 I drove for about 100 miles before I could get back home. I noticed that the car's behavior seemed to degrade during that time. Regeneration during braking and general use of the battery for acceleration seemed to be curtailed as time passed. Codes were cleared at home. Again block 10 voltage was lowest and internal resistance was highest.

On the other July dates the codes were cleared almost immediately. The car is now at home and I'm not driving it further. In no case did the RTOD disappear on its own.

The question now is how to proceed.

Jim x 3