Hybrid Battery Failure or Something Else?

I have a gen3 prius model year 2010 from japan (G Grade Touring Leather Selection) which is basically a Prius V with AT package, have been using it from almost brand new (<2000km) to now around 130000 km. Maintenance has been done regularly and a few months ago the car started showing some problems. The issue starts with a PCS (pre collision system) error along with a "Check Hybrid System" warning. The PCS warning light, check engine light and the orange warning triangle are displayed. When this happens, the engine remains always on from starting the vehicle to stopping without it shutting down while stationary or when cruising. But the power output is not severely affected or not affected since it runs normally with the engine, but with less FE in traffic driving. In highway driving, the average FE is almost as if the hybrid system is working with around 22km/l. When starting the vehicle too, before the engine turns on, the vehicle creeps forward, indicating the hybrid system does function at that moment, but in normal driving while the errors are displayed, the eco, pwr modes nor the energy flow displays function.
After visiting a Toyota dealer and resetting the error codes, the car functions perfectly normal without any issue after which around another few weeks the same problem occurs, which can only be reset upon using the OBD device. This has happened several times now in the same pattern though the only downside is the reduced FE and somewhat less power.
The Toyota dealer read the error code as the hybrid battery needing to be replaced. When tested, all the individual cells have a voltage of over 15.7V and the delta value too is smaller than 1.2V. But since the error shows a PCS error does it mean that its not the hybrid battery but something wrong with the PCS system? We reconnected and cleaned the RADAR unit too to see if it resolves the problem, and also turning off the PCS system after resetting the error codes, but still the error keeps occuring after few weeks.
So anyone with any ideas regarding what is the issue please help, because replacing the hybrid battery is not such a big deal considering how much the car has saved over its lifetime, but replacing it if its in good condition and still not solving the issue would be terrible. Or that i should just reset the error every time and keep running ,hoping nothing serious will happen.

Thanks everyone.

 

Yeah Checked the 12V battery too. It was recently replaced and again checked its voltage which is very much ok at 12.8V when stopped and 14V when started.
Just bought a new ELM327 Bluetooth device since old one was lost. Plugged it in and checked the fault codes and the data from extended PIDS obtained due to thanks to usbseawolf in Prius Chat.
The following code was present: P0A80 (Replace Hybrid Battery Pack)
I cleared the code and upon restarting, no errors appeared and the hybrid system works with the engine shutting down as usual. The difference is that the pulling power seems to have decreased in EV mode and lot of assistance being required from the engine, especially on inclines.

Then after observing and logging the data while driving after resetting the fault code, I kept the Vmax-Vmin on the display to continuously observe it to see if there was a problem, when the engine was on and during braking, the difference hovered between 0.1V and 0.2V.

BUT when running on the battery and accelerating, the difference started rapidly increasing, with most times it hovering between 0.5 to 0.8V. and then running for a slightly longer period of time without accelerating enough to let the engine start, the difference went upto 2.9V !!! but still no fault code was displayed.... but from this and the low power output, i think the HV battery is getting to the end of its lifetime. Now going to individually plot the graphs for the cells, tried it for a while, but almost all are evenly spaced so all cells are ageing i guess...

Any inputs before swapping the battery?

Whats still weird is why the PCS light started blinking and it showed a PCS system error??? When the error was present..the radar cruise did not work.. but the PCS worked as a vehicle cut off in front and the seatbelts retracted automatically..

 

yeah checked and cleaned the intake vents and fan regularly too. Recently had the corrosion on the bus bars also cleaned. Replaced spark plugs, cleaned injectors, done the whole lot, including replacing transmission (PSD) oil on time too... so no idea how this happened, just this january went on a 3000km trip and had a trip average of 27kmpl. (around 63mpg) so it cant have been that bad then..