the 09 rene and earlier models have a 450w magneto. The batteries are minimal sized. The winch, under load draws an astronomical amount of current and will drop the battery voltage in a blink.
Can AM's ecu has set points that are to remind you that you are depleting the battery, thus the light.
I have found that placing the quad in neutral and revving the engine up to 3k-3500 rpms will reduce this. When pulling someone else out, I tighten the line with the winch, then use the quad in reverse to pull them out, minimizing the use of the winch under load.
Also, I read somewhere that the can am will not provide a sufficient charge until about 4500 rpm's - not sure where.