An update on my Battery drain issue:
Over last weekend including the Friday the car was parked at home for ~60 hours and only lost 1 to 2% after being charged back up to 80%, which is normal behaviour I believe. Also when I charged the car up from 48% it showed when I arrived home, although it gained 2% to 50% SOC in 3 hours after I got home, to 80%, my Zappi showed that 18 KWh had been put into the battery. 18KWh is approximately 25% of the useable battery capacity, 48% or 50% plus 25% does not equal 80% and in reality there would be efficiency losses, making the discrepancy even greater. These facts suggest to me that the apparent loss of battery SOC is probably a BMS calibration issue.
Last week I only charged the car up to 70% overnight, so that when it was parked at work the SOC was ~55% instead of the normal 65%. This resulted in between 0% and 2% loss of SOC at work on each of Tuesday, Wednesday and Thursday. So I'm wondering if the constant repetitive charging and discharging to the same SOCs is affecting the BMS calibration, or may be it is just that last week the ambient daytime temperature was higher than the week before?