The only easy way is for you to buy the service manual - it is pretty hard to tell you how to service your regulator if you don't know what it is...
And it is - or at least something in the charging circuit.
Early Suzukis had consistent charging problems, resulting in run-down batteries, short battery life, hard starting and frequent stator and regulator/rectifier replacement. Some of the problem is due to poor quantity or corroded electrical connectors, some to a poor ground to the regulator/rectifier and some just poor quality components or design. Keeping the connectors on the three stator wires clean and by running a heavy ground wire directly from the negative terminal of the battery to the regulator/rectifier mounting bolt will help.
You can download the GR650 manual here
- just look for the tiny "Save file to your PC: click here" at the bottom right of the page.