Ignoring what manufacturers say (They are incredibly risk averse) and much of what they say is to cover themselves and give get out clauses, and the fact that we have these cars for 3 years on a lease and the battery warranties are usually around 8 years!
The preserved wisdom from people who actually drive EV’s is that once a month it is good form to charge to 100% as the Battery Management Systems does lots of work in the final 10% from 90-100% charge, managing and balancing out the cells, that final 10% often takes longer than it takes to go from 20-80%.
You also need to be aware that all batteries have buffers, so when the car shows 0% or 100% state of charge, the battery is actually nearer 5% and 95%, theses buffer zones are unusable to the car, but are there to protect from fully discharging and killing a battery.
AC (Slow) charging is believed to be healthier for batteries, but there are plenty of people (me included) who do that vast majority of charging via DC fast chargers, and are seeing no degradation of batteries (Taxis with well over 120k miles all on DC and battery still healthy). Currently I’m getting around 340 miles on a 100% charge.
The biggest thing personally to understand is how you car behaves to charging, and the benefits of different types of charging. I don’t think many new EV owners (Or dealerships) understand how the cars work. Take the Kona for instance, it has a 64kW (Usable) battery, and will charge at 11kw on AC and 77kW on DC, sounds great… But it will only charge at 77kW for a very short time and only at a specific battery state and temperature, if it’s not in the sweet spot, it will be much slower. The same goes for chargers, you are lucky to get much more that 44kW from a 50kW charger.
I do most of my charging on Ionity 350kW chargers and these are the average speeds I get:
unto 25% – 53kW
25%-53% – 77kW
54%-57% – 71kW
58%-73% – 58kW
74%-77% – 36kW
78%-90% – 24kW
On a long journey, I will only charge the car to 73%, after that it’s quicker to continue the drive to your destination (or next charging stop) than it is to stay on the charger. Once a month I will DC charge to 90% and then go to a free AC charger and top up to 100% to manage the BMS system. I never pay for AC charging, as there are plenty of free ones at supermarkets,
Back to the original post, the only real issue against regular charging on a granny charger is making sure that the electrics up to the socket are good, you will still be drawing 2.1kW for extended periods, and how long the granny charger will last (Unknown) but they are designed for occasional use, but I’m sure they will last for longer than the 3 year lease.
Previous Motability Cars
2006 - 2009 Skoda Superb VR6 2.0tdi
2009 - 2012 Citroen C5 2.0tdi VTR Nav
2012 - 2015 Nissan Qashqai 1.5dci tekna
2015 - 2018 Ford Kuga 2.0tdi Titanium X
2018 - 2021 BMW 220d X drive 2 Series Active Luxury
2021 - 2023 Hyundai Kona Electric Premium SE
2023 - Hyundai Kona Electric Ultimate