Apple Watch Ultra is also compatible with 45mm bands, but 45mm bands ought to only be worn for relaxed, each day wear. Screening done by Apple in August 2023 using preproduction Apple Watch Ultra two (GPS + Cellular) paired with an iPhone; all products tested with prerelease program. Battery lifetime https://allhealthmarket.com/product/aeahmarket/appleband/silicone-strap-for-apple-watch/apple-watch-strap-double-buckle-band-for-series-1-9-38-49mm-ultra-2-silicone-sport-strap/