Originally Posted by Reddleman

As a fixed rear light by Spanninga, the cover unclips from the black back when you change the batteries - details are shown here: https://brilliantbikes.co.uk/brompto...ear-light.html

The adaptor you linked is the kind that works with most clip on lights, I use a similar one on another bike with an old Cannondale branded led rear light that I picked up somewhere.