I've had heated grips on a BM before and they're OK but I tend to find that they get the palms of your hands really hot whilst the rest remains cold, even with handguards. Maybe down to my crap blood circulation !
However, there is a solution - heated gloves. I have a pair of Gerbings and they are amazing. Did not get cold hands once last winter. 100% waterproof too. One of those 'I can't believe I didn't buy them before' moments.
www.gerbings.co.uk I'd recommend the 3 way heat controller too