The timeline was different here in the UK. (Sorry for long post!)
There have been 4 BMS updates that I’m aware of.
November 2019, enabled timed charging of sorts - mainly only Ohme, Rolec didn’t work without a work around - trickle charge.
July 2020 that allowed the Rolec & other chargers to smart charge, plus would work if the car wasn’t locked. It also introduced an equalisation issue where the car could take many hours to balance the cells.
October 2020 This was an update to sort out the long equalisation times but introduced other issues, such that the cells would not balance at lower state of charges and resulted in range issues and also lack of power and regenerative braking especially when cold.
This update only really came to light when the temperatures dropped and we all found that our range had decreased dramatically, with some users only able to add 20+ kWh to an almost empty battery.
I understand this update was also applied to European cars at the same time as the battery heater update, so owners thought that the heater update was causing the drain, but I suspect because that the heater update isn’t causing the drain, but it is the duff BMS.
January 2021 This is the latest update which is supposed to rectify the issues introduced previously. We understand that it may take a few cycles with equalisation to get back to what it was like after the November 2019 update! The following is from the Israeli MG importer:
As a result of an inaccurate algorithm in the software installed in the vehicles on specific dates, an imbalance was created between the battery cells.
In practice - the battery management computer detects and stops charging when the first cell reaches maximum charge and sets this mode to about 100% charge
As a result, over time and depending on the nature of use and charging, a greater imbalance is created between the cells that the battery management computer did not correctly detect and did not reduce, which actually resulted in a reduction in the amount of energy the battery contains after a full charge and a reduction in the possible range of travel.
The update received from the manufacturer, and tested by us, updates the software of the battery management computer (BMS) and performs a slow procedure of balancing cells while using the vehicle and at the end of charging until reaching an optimal state.
The length of time it will take to reach the ideal balance varies and depends on the condition of the cell balance before the update, the nature and duration of use of the vehicle and charging each day. It is therefore necessary to coordinate an orderly appointment and examine the alternatives to the solution until the end of the treatment.”
I understand to get the car back to normal will take 50-100 hours of equalisation charging per10V out. 445-455V.
If your car is out by 20V, that will take at a guess 100-200 hours of equalisation charging to get back to 455V.
Equalisation charging is the bit after the car has finished charging to 100%, when the MG badge glows constantly.
The BMS i understand can only move around 1-2mV per cell per hour.
So, my takeaway is it’s going to take a while to sort out.
I understand that MG tested this by leaving it in ‘Ready’ overnight, then charged during the day and repeated a few times. Not many of us can do that though… if we want the car to be there in the morning!!!
What you can do to help speed this up is to charge to 100%, then discharge down to 93% and then charge up and balance. You don’t need to discharge the battery completely
There has also been a High Voltage Fuse update where the DCDC & TC modules were updated because a few vehicles just completely stopped for no apparent reason whatsoever, this was in August 2020.
There was a batter heater update for the Scandinavian countries to help alleviate coldgate where the car would only charge very slowly at a rapid charge due to the cold battery and ambient temperature, but this has very strict criteria to work where the minimum cell temperature has to be below 10C, the state of charge between 20% & 55% and the battery coolant has to be below 35C. It turns off as soon at the battery coolant temperature reaches 25C. When working you would expect to see around 20A current draw. The automatic heater still works when plugged into a rapid charger even if the heater is turned off.