HV battery SOC issue

Hi everyone, this is my first post, thank you so much for the endless info, that helped me a lot with multiple issues on my 2005 (299999km+). Last month my hv battery died and i decided i dint want to do te so called whack a mole repair. So i found a semi-new battery from a 2018 toyota, bought the 28 modules and replaced them all (using the old case of course). First few weeks the car ran fine, but now i have a curious issue. When i go on a long downhill, the car charges to "full" green bars, and when i start using the power, it almost instantly goes to a low SOC. Looking at hybrid assistant data, it seems that the car is incorrectly estimating SOC, because the module voltage never goes bellow 16v, eventually it will throw a p0a80, which goes away after i reset, only to return when the above pattern is done. While stationary, if i do a slow discharge, like using the ac at max cold, the battery seems to behave normally with a slow discharge. I have rechecked everything, torque the nuts again, cleaned the bus bars again, to no effect. Any idea of the root cause? Your help is appreciated!

 

Thanks for the replies.

yes, i checked the serial numbers, it was from a wrecked car. Also the newer modules (2016 and above, i believe) have a slightly different design in the top.

i did reuse the old wire frame, some voltage sensor tabs had some corrosion but none were broken. I also double checked the connections. Do you think it might be an issue with an intermitent bad voltage reading? When i drive the car, the drop from normal soc (50-60) to sometimes 30% is pretty much instant.
Thanks everyone

 

you mean the orange socket where all the voltage wires sensor conect? I didnt remove it, just checked it was righly connected, but i will check it.

yes, i did this using hybrid assistant, all modules are within 0.3 V. Also while stationary i performed the battery health check (the one with max ac), the battery lasts a long time without the engine cutting in. It seems to me that the problems begin when there is high charge current involved and battery gets "full" (ie a longish downhill where regen braking os used) From then on, the battery soc just crazily jumps arround.

 

searching the forum for possible issues i found this, and i noticed that my nuts are the old version (the left One on the picture). Does anyone know if a 2005 should have newer one? (The battery had been already messed with by previous owner)

 

Ok thank you, will try to remove the ecu and check

 

Checked ecu, no signs of corrosion. Do you guys think it can be the nuts on the terminals? They are quite black-ish, seems they lost the coating.

 

Thanks again for your replies

unfortunately i didnt record a trip before opening the battery, but here is attached a report from hybrid assistant (doing the ac max test)

i also think (and hope) this is the case. i have ordered the wire frame from toyota. You can see a picture attached, i cleaned the busbars but the nuts and voltage sensors are quite corroded. As you can see in the report, the middle cells have consistently lower voltages (min and max), so this may be an indication that the connections between modules is not good (?) (I reshuffled the modules before installing them, they were all showing the same voltage at that time)

 

1 month for toyota to get the parts (nuts are out of stock). If anyone in europe knows where i can find them (part 9291-47011) it is highly appreciated.

 

Follow up: new wire frames and nuts (all OEM), seems to have solved it. In the first few days after the repair it was still having the issue, im thinking maybe one module was not balanced, but after a while it was gone and the battery capacity improved a lot. Feels like brand new now (knocks on wood). Hopefully my next post is only when I reach 500k km. Thanks everyone for the help!

 

Follow up: it turns out one of the modules was bad but voltage only droped sneakly under severe load (full throttle or ev driving). Replaced that one. Battery has been good for 1year+