I put the FootWarmer inside a ZipLoc equivalent pouch with polyester wool for insulation and set the battery in the outside of the bag and put another pouch on top for rain insulation when it is needed. The wool encased the heater element and there was zero free air around it other than the one inside the wool. At 75 % power in 46F it was very warm and totally useful despite my dry skin so without rain in this temperature it is fine indeed. I was just able to shoehorn the setup into my Westside discs small bag side pocket. In this temperature after drying the disc and using an umbrella i should be able to warm the fingers enough for good grip but it is a hassle and the 30 second rule comes to play at times most likely. I can always add more insulation and use a larger bag to at least partially counter the dropping temperatures. The acid test for the current rig comes in colder weather and rain. For rains at this temperature i need to wait because i got cold today. But now i'm ready to declare at least a partial victory.
Another helping factor for this season beside using argan oil and more often than regular moistrurizers was buying a good 1 liter thermos bottle that is enough to keep me warmer for longer. It keeps the contents much hotter and much longer so the drink warms me up much better and having more hot liquid helps too except for output issues

And i was using water now instead of with a dash of cognac or brandy like in the previous two winters when i wasn't in competition.
I have to see if i could squeeze in a similar or the same setup of the FootWarmer into a jacket pocket. It seems to be too large without bending the leads to fit in any pocket i have now that is on the outside of the jacket. And inside pockets can't be used because opening up the jacket in colder weather is not possible with the temps we get here. I'd catch a cold or at least get too stiff and cold and miserable.
i can't predict below freezing operation but it sure has extended non real compromises playing season for me so it is definitely worth the price and effort for me. Staying a little warmer does not hurt either

I'm happy but cautiously so because i don't know just how far the benefits extend and i suspect i need to make a more insulated version for colder weather. Luckily i already own a thermal blanket so i have cheapo options available.
Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.