This is the little rubber terminal cover as featured on the Bosch Active / Performance frame mounted battery systems.
For Bosch systems from 2013-2016 (Works on some later models too). These only work on particular models with the frame mounted battery. Looks like this:-
Some particular brands will have their own integrated design. So make sure yours looks like the above to ensure correct fitment before ordering.
Great service and dispatched quickly. Shame it didn't fit my cube ebike though.
Not the one I wanted i,m afraid,it's the rubber cover from a 2016 haibike I required they look so similar.