Not sure what figures you are using wigwam, off peak octopus is 10p per kWh, so a full charge of a 60kw battery from empty would be £6, compared to £21 on standard peak of £0.35 plus on a 3 pin woukd take 12 hours plus compared to 6-7 hours with wall charger.
if you are just charging as and when you get home, you’re not really using the benefits available.
we run the dishwashers and washing machine on off peak too