P0138 2005 prius engine hesitation and maybe hv battery problems?

So my check engine light (plus two ! lights and a banner on the screen upon startup that says "problem") came on a few days ago and I just got the code read and it was P0138: oxygen sensor circuit high voltage (bank 1 sensor 2).

It's a 2005 prius with ~178500 miles on it, bought it from my grandparents in Florida who took really good care of it. The engine light turned on upon starting it on a super hot (90 degree) day after it had been sitting for like 2 days in similar heat. I just drove it on a 1000 mile road trip two weeks ago, also got the old changed right before the trip.

Currently, the engine hesitates to accelerate at low speeds or from a stop and from the energy monitor screen it appears as if the HV battery has no charge and isn't charging from the engine (battery icon is constantly at just one red bar). MPG is down from 40-45 to around 35.

Is my HV battery just dead or is this a side effect of another problem (O2 sensor or something related)? Any idea what could be wrong?

 

Yeah just got it diagnosed today, it's definitely the HV battery, unfortunately.