Check hybrid system

had the CHS light come on two months ago. Company came out and replaced four modules in HV battery. Light returned three weeks ago. Same company came out and replaced 4 more cells. Light didn't go out. Company returned and took battery off to their shop for a look. Returned battery three days later and CHS light came back after 5 miles of driving. Said company sent (new) employee back out but was unable to fix issue. Discounted repairs to 1/2 price due to (misdiagnosis?) inability to repair.
Same company has offered additional services but I feel three times is enough.
Took to dealer and they said needs battery but would require $500 in added troubleshooting to be sure.
Charged me 150 for this service (statement).

I have taken many engines from cars and even returned a few to their prospective locations. I've replaced alternators and head gaskets and even converted a few cars to newer motors. I'm confident that I could repair this w a little guidance. Removing the HV battery is not rocket science. Testing cells for voyage seems straight forward. Testing for load seems a bit more of a skill. Im assuming this is coming down the pike.

For those of you familiar w Prius troubleshooting and diagnosis what would be the next step. How do I confirm its the HV battery? I'm considering a rebuild kit ($1600) if the battery is indeed in need of replacement. Just not looking to throw parts at it w/o proper eval of current parts.
Looking to fix it myself and learn the Prius. Planning to drive this thing into the ground. Currently half way there at 178k on a 2010 Prius 5.

Thanks ahead.
Jay in Tucson.

 

No codes divulged.
I'll look at that thread.

 

I think I'll at least go thru and see what codes ive got and Poss test the modules for consistency. If it's not the battery I don't want to buy one.
Sounds like fun to put it apart and start testing things.
Does one need anything special to read the codes? I know FLAPS can do the basics but they appear lost for the most part (if it's not an option on the screen your SOL).
I'll look into tech stream software.