Amazon's new Battery Bases make your Echo speakers portable | What Hi-Fi?
Dot 4th/5th Generation Battery Base (Dot 4&5 not Included) Dot Battery Base Accessories,Power Supply 6 Hours playtime, Black: Amazon.co.uk: Electronics & Photo
Battery Base for Dot 3rd Generation, Portable Charging Power for Dot 3rd, Speaker Dot Auxiliary Power Accessories (Not Include Speaker) (White-37W): Amazon.co.uk: Electronics & Photo
Turn your Echo Dot into a portable smart speaker for $27 - CNET