There’s much higher charging losses on a granny, you don’t get all the watts you use…and they typically charge at 10a, not the 13a you assume. So you’d get 2.3kw per hour before losses, probably lucky to see 2kw after losses, or 16kw supplied for a spend of 18.4kw.
7kw chargers also have losses, but they are a bit less and not so noticeable as a much lower % of overall consumption.
Plenty of data on this on Speak EV.
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