Warm hands are a necessity for training in the winter. Going out to test gear, stay proficient, and work out winter concealment issues isn't nearly as much fun (or productive) with chilly digits.
Enter the new age! Disposable hand warmers are fairly common, but the rechargeable ones are pretty darn good as well. The particularly one I went with, the Jomst brand, has a large battery capacity, a reasonable size for pockets, and three heat settings. On top of all this, it can also be used as an emergency charger for other electronic devices.
I highly recommend a reusable hand warmer. It makes those cold days on the range a little more tolerable and helps us keep sharp in the winter months.
Here is a link for the one I purchased: https://www.amazon.com/dp/B07WWLD3L2/ref=cm_sw_r_cp_apa_glt_fabc_H0DBGEQH6CCEHTR6RBVV