Heated grips may be switched off. But headlight must remain on.
My 50cc has a 85W alternator (and H4 55W). When idling, the head light flickers opposite to the indicators (2x10W). Tail light, instruments and sometimes the brake light want their share too. Forget heated grips/seat bench and radio/stereo with speakers.
The 650cc has 400W and basically the same lights (energy consumption). Could handle a SatNav too.