It is interesting to hear from someone else in a similar situation.
My HV battery is still looking good, I am targeting 345V (115V per module). I used 3 x 60V Lab PSUs borrowed from work to get the all cells to ~ 3V evenly by serial linking the PSUs. I then connected all the modules together and I'm now using a 400V 1A PSU I bought (HSPY-400-01) current limited at 500mA to get to the target. (I am at 315V at the moment)
I could not retrieve the P18051C code when the HV battery was in the car but I am going to make a few cable extensions to test the HV battery without physically re-installing it in the car and see if the P18051C code is there.
If it is I will send it off to be fixed.
There are a few Youtube videos showing the ability to access the BMS/HV battery data using Canbus and Vediamo which I would also like to try.
I have a question to ask if I may.
Do you know what triggered your HV battery to deplete in the first place?
My 12V battery went flat rather quickly after the HV battery was removed, I charged the 12V battery and fitted it back into the car with a wireless current and voltage transducer. The info is sent to a small display outside the car which I can see easily. If I open the car with the remote I can see the current jump up to 16A briefly as various systems become active and then drop down to almost zero when locked. A week has passed and nothing unusual has happened but I will continue to monitor this.
The voltage is dropping slowly < 0.1V per day