I too tried heated grips some years ago,same problem.I now have Hand guards and use Keis heated inner gloves.They keep all the hand and fingers warm.Not super hot but tolerable even in low temps.I always buy my Winter gloves one size Bigger to accommodate inner gloves.
Also core body temperature is important so I have a homemade heated breastplate made out of stiff Bubble wrap with a couple of flat cheap heat pads on it and tuck it under my jumper.All powered through wires run through my Riding jacket.
Cold Weather food tip.Have a bowl of porridge(I use those quick Sachet ones) if you are going out for a Winter ride/commute.Porridge is a slow release food and will keep the core body temp up for hours
HTH