I too suffer with bad circulation in my hands, Reynauds syndrome, and I use a pair of heated inner gloves from warm n safe if I remember correctly.
They plug into the bike and once you have faffed around running the wires down your jacket sleeves they are simple to connect and disconnect when getting on and off the bike. I have forgotten before and they just unplugged as I walked away.
There are 5 heat settings and I have never needed more than 3. That said being just outside Sydney it doesn’t get that cold, but I have used them down to 0deg C.
I find the advantage with liners is that when it warms up I just take them off, store them on the bike, and use my normal gloves.
Over here the temps can vary from 0 to 20+ in the same day, so liners provide a better level of versatility.
The other issue with battery packs is the degrading life cycle, and if your out bush for a few days may not have the opportunity to charge them.