Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially and if have not been tried; inspect the battery & ground lines and/or check/clean the battery cables + terminals as a preliminary consideration. Better yet, have the battery externally charged and then LOAD TESTed (even if new and just for the purpose of eliminating it as a suspect).
Still, proposed checks & tries (if have not been done):
All other checks would be with the use of a multi-meter.