They enable your speakers to be used wirelessly - ideal for taking them outside in the summer ahead.
Made by Mission Cables, the battery bases have been available in the US since the end of last year, but have now arrived in the UK too.
A base for the 4th gen Echo costs £39.99 and offers up to five hours of playback time on a single charge.
You just secure the base to the bottom of your Echo with a thumb screw. It sits the Echo into a cradle that doesn't compromise audio quality.
As well as give you the freedom to put your speaker anywhere in the home, it means you can take Alexa on the go with you. You just need a Wi-Fi signal (or wireless hook up to a mobile hotspot or phone).
The simple design includes an LED battery indicator which tells you when you will need to recharge it.
It's all fairly ingenious and an ideal answer for those who already own one of the supported Echo devices. Otherwise, the Sonos Roam has also recently been announced to offer Alexa (and Google Assistant) support on your travels.
That will be available from 20 April 2021. The battery bases are available now.