The charging system has 3 basic parts:
1. Stator/rotor has the ability to keep the bike running; as long as the rpm puts out the AC. The lower the rpm, the lower the voltage output, goes poop with a pop. So you associate the slowing down as you rolled up, you got there, it's putting out so it's not the stator-rotor.
2. Vo/Reg has the ability to DTT the excess volts to ground or the AC would have blown the bulbs with that kind of volt against the watt of the bulbs, meaning, it can control and regulate the input and deliver the proper output, it's not the voltage regulator.
3. Battery has the ability to act as a resistor. So even though the battery lost the amperage or can no longer store said demand to push the starter motor over, the surface output of the stator/vo-reg can keep the black box, coil, lights going at a certain rpm threshold. But when the rpm drops, this is where the battery keeps feeding 12v out to the black box, but cannot even push 12v out of the battery. So getting you to camp, then home, it shows 1 and 2 are performing their tasks, so it narrows it down to the battery.
Make sense we narrow down 3 simple variables?