Well I agree with fazt that the damage to the fuse and overcharging can result from a faulty rectifier. And for reality's sake, let's clarify WHY this would happen..
A faulty rectifier would result from the internal circuit components failing. Rectifiers convert the AC signal produced by charge coils to DC via a specific configuration of diodes which are basically NOT functions in a circuit, meaning they only allow current to pass in one direction filtering out the smooth sinusoidal property of the AC signal into a jagged/peaky DC signal. This must be smoothed by the capacitors prior to output to properly maintain the battery, if not, those high peaks will damage or overcharge the battery. Capacitors store charge and therefore are capable of discharging at rest, this risk of shock necessitates resistors to be connected to safely discharge the capacitors, happens in less than a second after turning the motor off. All this of course is not important for troubleshooting because a faulty rectifier must be replaced and people don't care about the inner workings of rectifiers circuitry because it works or it doesn't. The simple explanation is a damaged fuse or overcharging, and fix is check connections and/or replace the rectifier. I prefer to understand the why, and this sometimes requires actually understanding what is happening inside these small electronic components, because I guarantee you it's not just smoke and mirrors, in reality there are such things as diodes, capacitors, and resistors inside a rectifier (Google it).
