2008 Prius HV battery ailing at 360000km

my 2008 Prius has been a delight to drive, with minimal maintenance required since I bought it used with about 113000km on the clock. Now it has done 360000km.

Yesterday I have had the first 'Replace HV Battery' Triangle of Doom ( P0A80 - Powertrain )

Torque Pro shows me that HVB02 has almost always the lowest voltage and it's voltage drops to 1.2V less than the rest under heavy acceleration. So there is either a dying cell or a severely imbalanced cell in that Block 02. And it needs some attention to prevent it from deteriorating rapidly.

I have extensive, but very rusty experience from keeping several NHW10's going for years, I miss the Turtle when this happens. But I'm not looking forward to repeating the all-consuming task of nursing a failing battery pack for years.

What I also miss is the ability of the NHW10 to perform a forced trickle charge by putting the car in 'D' and then keep a foot on the break and the other foot on the gas pedal, fully down. It does seem to charge the battery to 84% SOC maximum in the NHW20, but no further.

I know that regular 0.6A trickle charges might keep the HV battery going for a long time, and at 360000km I might get away without replacing anything before the car is uneconomical to maintain.

My questions are these:

Is there a way to make the NHW20 perform an in-built overcharge of the HV battery, with or without Torque Pro, like the NHW10 could do?

What thread on this forum has already discussed very similar issues? I can't seem to find one.

What thread on this forum is a good read for learning how to access the HV battery just enough to attach a trickle charger and possibly drive the 12V cooling fan? I have built a charger for the NHW10 which measures the thermistor-like sensors on each cell and powers the cooling fan and disconnects when cell temperature rises. It shows voltage and current and is relatively safe, using an isolating transformer as the first stage. I could quite easily change the motor drive capacitor of the charger to achieve about 0.6A current desired for a trickle charge of the smaller NHW20 battery.

Thanks for any help with this!

Mik

 

Thank you very much, that's exactly what I needed!

 

The cell in Block 02 deteriorated rapidly, almost constantly at zero V or even reversing a bit.

After reading a few posts here I decided to buy a new battery from Toyota and I just brought it home.
AUD2477.12 without installation. Toyota want AUD600 for installation, the warranty is 2 years on the part no matter if they install it or someone else. So I'll do it myself, looks like an easy AUD600,- to be saved.

I stood the battery box on one of it's small sides for about 10-20 seconds, can that cause problems with electrolyte spilling?

What do others think about keeping and repairing the old battery vs getting the AUD500 refund from Toyota? I have 5 Toyota battery modules with silver sides, which I bought used maybe 10 years ago. They may or may not be a reasonable match for the failed module in the old HV battery.

 

Thanks SFO!
I'm trying to work out if this is actually the correct battery.

 

I had a closer look side by side and I think it is the correct battery. But as you say, it needs to be taken apart and assembles, some parts (cables) came with the new battery, many other parts need to be transferred from the old to the new battery (vents, air baffles, electronics).
I did not order a part number, i just told them I need a new battery for my car and they looked up the car using the registration number..

 

I have installed the new battery and the car is running again.
The old battery has a lot of 'stuff' built up on the bus plates, I'm not sure I want to do anything with it, other than get AUD 500 from Toyota.
Why do Toyota pay AUD500 for the old batteries? I read somewhere that it is because they want to re-use the electronics, but once a new OEM battery has been made usable by transferring the needed parts from the old battery, there are no valuable parts left on the old battery. None that I can see, anyway.

What are the 2 openings with 'filter' material on the intake cooling air duct good for? The main intake from the cabin (on the side of the rear seat) has no filter, but there are 2 holes (with some non-woven fabric covering them) hidden behind the trim panels.

 

It was the correct battery and the car runs well with it. Remains to be seen if the oil consumption reduces (as others have reported).
I sent the old battery back to Toyota, I just don't have the time to work on it at the moment. I did too much of that when no replacements for the NHW10 were available, kept it running for years, but for AUD1977.12 and a few hours work (the 2nd time will be much faster now that I know how) it's not worth it for me right now.
I'm on the East side of Oz, so shipping it to Perth would not be a good option.