Buy GIRA + Senic Friends of Hue Outdoor Smart Switch | Compatible with Philips Hue (No Batteries, No Charging) | Wireless Smart Home Light Switch & Dimmer Made in Germany | Homekit
Battery for Philips Hue Dimmer Switch - 2 Pack New | eBay
Battery problems with the Hue Smart Button: Button cell empty in a few days - Hueblog.com