I'm sorry, but there seems to be some misunderstanding of electrical theory going on here. The website says it has an 85kW (peak?) motor but only a 17
kW hour battery pack - although they call it "Dual Redundant" without specifying what that means. There will always be losses involved when re-charging a battery (particularly at high charge rates), so call it 20 kW hours of power needed for a full charge. The most you can draw from a UK 13 amp socket is about 3 kW - 13 amps x 230 volts = 2990 watts, so you would need a MINIMUM OF 6½ hours if limited to using one of those. To get 20 kWhrs in one hour (never mind less) will require 87 amps, or more than most single phase supplies are fused at... The only realistic way of meeting that sort of demand is from a 3 phase supply, and even then it will still be a significant load for any typical rural flying club scenario.
I note they claim the battery is:
"Designed to be quickly replaceable within minutes"
which answers one of the questions posed earlier.
They also say:
"The WATTsUP is optimized for traffic-pattern operations, where 13% of energy is recuperated on every approach, increasing endurance and at the same time enabling short-field landings"
This implies the motor will become a generator during the descent, and is going to be the equivalent of having reverse pitch on a conventional aircraft. Hence the "Short field landings"!!! But this will be a VERY different experience to students than the "glide" performance of the usual spamcan on idle, the engine of which is still producing significant thrust... Even my old flexwing behaved noticeably differently with the engine switched off.