Next: Charge the battery. Even if it is damaged it should work for testing.
Do the short-circuit or leakage test from the service manual. With the bike off, take a multimeter, set it to the highest current rating (10 or 20 amps?), connect it between the negative battery cable and the negative battery terminal. Turn the amp rating down until a measurable reading shows. It is important to know exactly what the reading is, and it should be .003 A / 3 mA or less. If the current is higher, pull fuses until it plummets and that identifies a circuit with a short. Find out what circuit it is and troubleshoot the devices on it.
My opinion is to use OEM charging parts. Others can get the electrical part right but I question if even some of the leaders understand the punishment of heat, vibration, and corrosion that motorcycles generate. So many failed Rick's stators...