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What you describe is exactly how it is stored. It's not a cheap bike, hence the Bosch motor. I expect corrosion to happen on bikes used daily in the UK, but the kickstand was disintegrating far quicker than I have ever seen. Interestingly, the kickstand isn't used whilst charging as the bike is locked to a wall anchor, but as you say it's looking exactly like a sacrificial anode on a boat would.
Stop using immediately. Seek professional advise.
Non professional advise...... If its a cheap bike then corrosion on all sorts is going to hapoen. Best uk outdoor storage solution is to be protected from above and the back from weather, but with front open. A lean to against shed to stop almost all the rain falling on it and then plenty of air flow so it will dry asap. Avoid waterproof covers.
If could be a slight anoidic affect caused by the electrical fault causing extra corrosion (like a boat). What bike is it exactly?