@xssfox One thing I've seen discussed about running EV chargers off outdoor 10A sockets (although that's starting at 2x the power) is that many older outdoor GPOs have quietly been oxidising for decades, and aren't really ready to run continuously for many hours.
Probably more of a problem at 10A than 3.5A though (and I reckon it's one of the reasons that new cars seem to often come with 6A or 8A slow chargers nowadays.)