Code POB42

My 2010 Prius came back from the dealer after getting a new spark plug coil, it was running really rough so ! went to the closest dealer and they fixed the rough running part. The engine runs great now but I have the check hybrid alert light on along with all the other warning lights, check engine, triangle of death, traction control. My harbor freight code reader came up with only one code
POB42
Hybrid battery voltage sense "B" circuit low

Is there any way to isolate and test that circuit?
What voltage should it be?
They want to replace the battery and Hybrid battery voltage sensor for around a small $3600
That price doesn't hurt if you say it real fast!
I have disconnected both batteries overnight. The 12v test good on a load tester and 12.6v with a meter

 

Update
Pulled hybrid battery, cleaned busbars, they had medium corrosion.
tested individual cells all 8.16v or within .02v of that
cleaned fan, not too dirty.
Same code coming up.
Same triangle of death.
Thinking about replacing the voltage sensor.

 

Thank you ChapmanF.
The information you provided was correct, the sensor wires were not making a connection. I put an ohm meter on the sensor wire harness ant all the wires tested good. the problem was the connection inside the voltage sensor. I will be getting a replacement sensor and will update after that.
Thanks again everyone.

 

Replaced the sensor with a used one found on ebay. under $100USD.
The lights in the dash are now back to normal, no trouble. I believe that the problem is fixed.
Thanks everyone.