Before I went ahead to buy a box of fuses, I decided to try an experiment. I switched out the broken fuse with one of the remaining working fuses. The idea was to see if the only reason why the charging wasn't working was due to that fuse. Removing some other fuse was going to cause an issue elsewhere, but it if the charging worked, then at least I could buy fuses with confidence that replacing them would fix the problem.
That didn't work. So I took another look at the bike and this is what I saw in the space between the batteries and the charging box:
If it's not clear from the picture, there quite a lot of melted insulation in there. Alas, that's nothing that a simple replacement fuse will fix.
Over a year ago, Adan wrote this:
The problem, I was told, was the connectors to the charger. They melted. I was told this is a "known problem," the solution to which is to install more robust connectors.
I wonder if I 'm having the same issue that Adan was talking about. I hope the procedure for replacing those wires is well established, and it will be a simple task to replace the melted connections.