25/11/2025
So! The grand finale to an interesting process, the Tesla Model 3 HV battery upgrade. On paper it's a straight forward process, but then in reality some curve balls were thrown into the mix.
The HV battery swap itself was heavy work but mechanically straight forward. Here in the challenges start appearing one by one....
First off, the brand new 16v Lithium ancillary battery was drained over night meaning it needed to be recharged with a special charger so that it's internal mosfet transistor closed to let voltage flow back to the terminals. Without a 16v supply to the cars low voltage architecture the car wouldn't and won't function, this was needed to be operational so that a software update and CanBus redeploy could be carried out for the vehicle to recognize it's new and different HV battery.
HEVRA has been an amazing source of information throughout this process and to work with it took some time to work through the issues this car had as it wasn't an "off the shelf" type of repair.
Following that part of the journey it was then discovered that when the car had it's visit to a Tesla dealership in Leicester, one of the technicians had unplugged 2 of the main coolant pumps for the HV battery and rear drive inverter. And for good cause too, as one had completely failed and the other was running full tilt to compensate which had problems with its bearings internally.
Eventually after replacing these coolant pumps I could follow Tesla's own repair plan to bleed and purge the huge coolant system so it was free of air locks. In this instance I would say that I was less than impressed with this part and had to think outside of the box and put a dab of my own ingenuity into the process.
I'm thankful to say that the car is now complete and back in the hands of a very happy owner, who had bought the car in this condition with the intent on upgrading the battery for the newer more reliable type he has now.
